[glib: 1/2] meson: Don't misdetect stpcpy on windows platforms on clang

[Philip Withnall <pwithnall src gnome org>]

commit 1b94bfbd72dbbfb696fa68f3742f40998096b438
Author: Martin Storsjö <martin martin st>
Date:   Tue Mar 31 23:54:17 2020 +0300

    meson: Don't misdetect stpcpy on windows platforms on clang
    
    See https://github.com/mesonbuild/meson/issues/3672 and
    https://github.com/mesonbuild/meson/issues/5628 for explanations
    of cases where meson misdetects functions due to clang builtins (that
    always are available, regardless of whether the platform actually
    provides them).
    
    The same also happens on GCC 10, which added support for __has_builtin.

 meson.build | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)
---
diff --git a/meson.build b/meson.build
index b13739792..2af71c38b 100644
--- a/meson.build
+++ b/meson.build
@@ -554,13 +554,23 @@ foreach f : functions
   endif
 endforeach
 
-# Check that stpcpy() is usable; must use header
-if cc.has_function('stpcpy', prefix : '#include <string.h>')
+# Check that stpcpy() is usable; must use header.
+# cc.has_function() in some cases (clang, gcc 10+) assumes that if the
+# compiler provides a builtin of the same name that the function exists, while
+# it's in fact not provided by any header or library. This is true for
+# stpcpy() on Windows using clang and gcc as well as posix_memalign() using
+# gcc on Windows. Skip these checks on Windows for now to avoid false
+# positives. See https://github.com/mesonbuild/meson/pull/7116,
+# https://github.com/mesonbuild/meson/issues/3672 and
+# https://github.com/mesonbuild/meson/issues/5628.
+# FIXME: Once meson no longer returns success for stpcpy() and
+# posix_memalign() on Windows using GCC and clang we can remove this.
+if host_system != 'windows' and cc.has_function('stpcpy', prefix : '#include <string.h>')
   glib_conf.set('HAVE_STPCPY', 1)
 endif
 
 # Check that posix_memalign() is usable; must use header
-if cc.has_function('posix_memalign', prefix : '#include <stdlib.h>')
+if host_system != 'windows' and cc.has_function('posix_memalign', prefix : '#include <stdlib.h>')
   glib_conf.set('HAVE_POSIX_MEMALIGN', 1)
 endif