stdio: fix probe on mingw under gcc 5.1

Per https://gcc.gnu.org/gcc-5/porting_to.html, gcc 5.1 intentionally
changed the preprocessor to emit multiple lines, rather than one
line, when expanding text that includes literal markers combined with
a macro expansion obtained from a header.  This in turn breaks the
probe for whether mingw headers support GNU-style "lld" for PRIdMAX,
as the probe text was no longer on one line.

This patch changes from grepping preprocessor output (with its
indeterminate layout due to differences in preprocessors) to instead
using a compile-time check of the length of the macro expansion.

It feels a bit gross, but the grossness is limited to mingw, which
is the only platform where using __gnu_printf__ instead of __printf__
will make a difference.

Based on a report by Suren Hajyan.

* m4/stdio_h.m4 (gl_STDIO_H): Change to compile test, to work
around new gcc preprocessor rules.

Signed-off-by: Eric Blake <eblake@redhat.com>

0 files changed, 0 insertions, 0 deletions