Re: C23 support in Autoconf

[Florian Weimer]

* Alan Coopersmith:

> https://gitlab.freedesktop.org/xorg/driver/xf86-video-vbox/-/commit/b66441a27fa85e2a3b63f10a0a5a846344327042

This change:

 #ifndef __cplusplus
+#if __STDC_VERSION__ >= 199901L
+#include <stdbool.h>
+#else
 typedef enum
 {
     false = 0,
     true
 } bool;
+#endif
 # define RT_C_DECLS_BEGIN
 # define RT_C_DECLS_END
 #else
 # define RT_C_DECLS_BEGIN extern "C" {
 # define RT_C_DECLS_END }
 #endif

is not really ABI-compatible with the previous C version (although it
restores ABI compatibility with the C++ version).  Is this an installed
header?

I expect that quite a few projects will encounter problems like this
one.

Thanks,
Florian