xwayland: Correctly detect whether posix_fallocate exists

We had HAVE_POSIX_FALLOCATE checks, but no such macros were ever
defined anywhere. This commit makes it so that this macro is defined if
the posix_fallocate is detected during configure.

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>
Reviewed-by: Julien Cristau <jcristau@debian.org>
(cherry picked from commit a2c3c34b44)

configure.ac

@@ -218,7 +218,8 @@ AC_SUBST(DLOPEN_LIBS)
 dnl Checks for library functions.
 AC_CHECK_FUNCS([backtrace ffs geteuid getuid issetugid getresuid \
 	getdtablesize getifaddrs getpeereid getpeerucred getprogname getzoneid \
-	mmap seteuid shmctl64 strncasecmp vasprintf vsnprintf walkcontext])
+	mmap posix_fallocate seteuid shmctl64 strncasecmp vasprintf vsnprintf \
+	walkcontext])
 AC_REPLACE_FUNCS([reallocarray strcasecmp strcasestr strlcat strlcpy strndup])
 
 AC_CHECK_DECLS([program_invocation_short_name], [], [], [[#include <errno.h>]])

hw/xwayland/xwayland-shm.c

@@ -24,6 +24,10 @@
  * SOFTWARE.
  */
 
+#ifdef HAVE_CONFIG_H
+#include <dix-config.h>
+#endif
+
 #include "xwayland.h"
 
 #include <sys/mman.h>

include/dix-config.h.in

@@ -518,4 +518,7 @@
 /* Define if no local socket credentials interface exists */
 #undef NO_LOCAL_CLIENT_CRED
 
+/* Have posix_fallocate() */
+#undef HAVE_POSIX_FALLOCATE
+
 #endif /* _DIX_CONFIG_H_ */