test_gdb now skips tests if it detects that gdb failed to read debug
information because the Python binary is optimized.

python-gdb.py now checks for "take_gil" function name to check if a
frame tries to acquire the GIL, instead of checking for
"pthread_cond_timedwait" which is specific to Linux and can be a
different condition than the GIL.

This fixes the exception '`ValueError: invalid literal for int() with base 10`
if `str(gdbval)` returns a hexadecimal value (e.g. '0xa0'). This is the case if
the output-radix is set to 16 in gdb. See
https://sourceware.org/gdb/onlinedocs/gdb/Numbers.html for more information.

bpo-37151: remove special case for PyCFunction from PyObject_Call

Alse, make the undocumented function PyCFunction_Call an alias
of PyObject_Call and deprecate it.

As it changes the way functions are called, the PEP 590 implementation
skipped the functions that the GDB integration is looking for
(by name) to find function calls.

Looking for the new helper `cfunction_call_varargs` hopefully fixes the
tests, and thus buildbots.

The changed frame nuber in test_gdb is due to there being fewer
C calls when calling a built-in method.

python-gdb.py now handles errors on computing the line number
of a Python frame.

Changes:

* PyFrameObjectPtr.current_line_num() now catchs any Exception on
  calling addr2line(), instead of failing with a surprising "<class
  'TypeError'> 'FakeRepr' object is not subscriptable" error.
* All callers of current_line_num() now handle current_line_num()
  returning None.
* PyFrameObjectPtr.current_line() now also catchs IndexError on
  getting a line from the Python source file.