Fix incorrect detection of '-Wstrict-prototypes' option

Revert "Simplify AC_LBL_CHECK_COMPILER_OPT a bit."
(commit 43e88cd5b8e9d9d643bbad585743123492452041)

The problem shows itself because 'configure' displays
"checking whether the compiler supports the -Wstrict-prototypes option... no"
even if '-Wstrict-prototypes' option is supported.

Moreover:
Update configure accordingly.
Fix a trailing space.

2 files changed, 79 insertions, 12 deletions

diff --git a/aclocal.m4 b/aclocal.m4
index 7c6d5b24..a50c2f0b 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -219,6 +219,36 @@ AC_DEFUN(AC_LBL_C_INIT,
 ])
 
 dnl
+dnl Check whether, if you pass an unknown warning option to the
+dnl compiler, it fails or just prints a warning message and succeeds.
+dnl Set ac_lbl_unknown_warning_option_error to the appropriate flag
+dnl to force an error if it would otherwise just print a warning message
+dnl and succeed.
+dnl
+AC_DEFUN(AC_LBL_CHECK_UNKNOWN_WARNING_OPTION_ERROR,
+    [
+	AC_MSG_CHECKING([whether the compiler fails when given an unknown warning option])
+	save_CFLAGS="$CFLAGS"
+	CFLAGS="$CFLAGS -Wxyzzy-this-will-never-succeed-xyzzy"
+	AC_TRY_COMPILE(
+	    [],
+	    [return 0],
+	    [
+		AC_MSG_RESULT([no])
+		#
+		# We're assuming this is clang, where
+		# -Werror=unknown-warning-option is the appropriate
+		# option to force the compiler to fail.
+		#
+		ac_lbl_unknown_warning_option_error="-Werror=unknown-warning-option"
+	    ],
+	    [
+		AC_MSG_RESULT([yes])
+	    ])
+	CFLAGS="$save_CFLAGS"
+    ])
+
+dnl
 dnl Check whether the compiler option specified as the second argument
 dnl is supported by the compiler and, if so, add it to the macro
 dnl specified as the first argument
@@ -227,7 +257,7 @@ AC_DEFUN(AC_LBL_CHECK_COMPILER_OPT,
     [
 	AC_MSG_CHECKING([whether the compiler supports the $2 option])
 	save_CFLAGS="$CFLAGS"
-	CFLAGS="$CFLAGS $ac_lbl_cc_force_warning_errors $2"
+	CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error $2"
 	AC_TRY_COMPILE(
 	    [],
 	    [return 0],
@@ -942,6 +972,7 @@ AC_DEFUN(AC_LBL_DEVEL,
 	    # Skip all the warning option stuff on some compilers.
 	    #
 	    if test "$ac_lbl_cc_dont_try_gcc_dashW" != yes; then
+		    AC_LBL_CHECK_UNKNOWN_WARNING_OPTION_ERROR()
 		    AC_LBL_CHECK_COMPILER_OPT($1, -Wall)
 		    AC_LBL_CHECK_COMPILER_OPT($1, -Wmissing-prototypes)
 		    AC_LBL_CHECK_COMPILER_OPT($1, -Wstrict-prototypes)
diff --git a/configure b/configure
index 822c1abe..db3780a9 100755
--- a/configure
+++ b/configure
@@ -3352,7 +3352,7 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -ffloat-store option" >&5
 $as_echo_n "checking whether the compiler supports the -ffloat-store option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	CFLAGS="$CFLAGS $ac_lbl_cc_force_warning_errors -ffloat-store"
+	CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -ffloat-store"
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -7656,10 +7656,46 @@ rm -f os-proto.h
 	    #
 	    if test "$ac_lbl_cc_dont_try_gcc_dashW" != yes; then
 
+	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler fails when given an unknown warning option" >&5
+$as_echo_n "checking whether the compiler fails when given an unknown warning option... " >&6; }
+	save_CFLAGS="$CFLAGS"
+	CFLAGS="$CFLAGS -Wxyzzy-this-will-never-succeed-xyzzy"
+	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+return 0
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+
+		{ $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+		#
+		# We're assuming this is clang, where
+		# -Werror=unknown-warning-option is the appropriate
+		# option to force the compiler to fail.
+		#
+		ac_lbl_unknown_warning_option_error="-Werror=unknown-warning-option"
+
+else
+
+		{ $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
+
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	CFLAGS="$save_CFLAGS"
+
+
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wall option" >&5
 $as_echo_n "checking whether the compiler supports the -Wall option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	CFLAGS="$CFLAGS $ac_lbl_cc_force_warning_errors -Wall"
+	CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wall"
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -7691,7 +7727,7 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wmissing-prototypes option" >&5
 $as_echo_n "checking whether the compiler supports the -Wmissing-prototypes option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	CFLAGS="$CFLAGS $ac_lbl_cc_force_warning_errors -Wmissing-prototypes"
+	CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wmissing-prototypes"
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -7723,7 +7759,7 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wstrict-prototypes option" >&5
 $as_echo_n "checking whether the compiler supports the -Wstrict-prototypes option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	CFLAGS="$CFLAGS $ac_lbl_cc_force_warning_errors -Wstrict-prototypes"
+	CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wstrict-prototypes"
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -7755,7 +7791,7 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wwrite-strings option" >&5
 $as_echo_n "checking whether the compiler supports the -Wwrite-strings option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	CFLAGS="$CFLAGS $ac_lbl_cc_force_warning_errors -Wwrite-strings"
+	CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wwrite-strings"
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -7787,7 +7823,7 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wpointer-arith option" >&5
 $as_echo_n "checking whether the compiler supports the -Wpointer-arith option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	CFLAGS="$CFLAGS $ac_lbl_cc_force_warning_errors -Wpointer-arith"
+	CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wpointer-arith"
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -7819,7 +7855,7 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wcast-qual option" >&5
 $as_echo_n "checking whether the compiler supports the -Wcast-qual option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	CFLAGS="$CFLAGS $ac_lbl_cc_force_warning_errors -Wcast-qual"
+	CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wcast-qual"
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -7851,7 +7887,7 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wshadow option" >&5
 $as_echo_n "checking whether the compiler supports the -Wshadow option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	CFLAGS="$CFLAGS $ac_lbl_cc_force_warning_errors -Wshadow"
+	CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wshadow"
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -7883,7 +7919,7 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wdeclaration-after-statement option" >&5
 $as_echo_n "checking whether the compiler supports the -Wdeclaration-after-statement option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	CFLAGS="$CFLAGS $ac_lbl_cc_force_warning_errors -Wdeclaration-after-statement"
+	CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wdeclaration-after-statement"
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -7915,7 +7951,7 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wpedantic option" >&5
 $as_echo_n "checking whether the compiler supports the -Wpedantic option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	CFLAGS="$CFLAGS $ac_lbl_cc_force_warning_errors -Wpedantic"
+	CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wpedantic"
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -7947,7 +7983,7 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -W option" >&5
 $as_echo_n "checking whether the compiler supports the -W option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	CFLAGS="$CFLAGS $ac_lbl_cc_force_warning_errors -W"
+	CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -W"
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */