Without this change, compiling with gcc and pedantic generates warning:
ISO C does not allow extra ‘;’ outside of a function.

allocations: test for overflow of requested size

Make our overflow checking look more like gcc and clang's, so that
we can substitute it out with the compiler instrinsics on platforms
that support it.  This means dropping the ability to pass `NULL` as
an out parameter.

As a result, the macros also get updated to reflect this as well.

Fix build warning on Android

Ensure that the given length to `p_read` is of ssize_t and ensure
that callers test the return as if it were an `ssize_t`.

Introduce some helper macros to test integer overflow from arithmetic
and set error message appropriately.

Always do a time_t cast on st_mtime. st_mtime on Android is not
the type of time_t but has the same meaning which is the number
of seconds past epoch.

Checkout performance