[glib/wip/baedert/fallthrough-clang: 295/295] macros: Define G_GNUC_FALLTHROUGH for more compilers

[Timm Bäder <baedert src gnome org>]

commit f04fff0309bd9c0819e630c7940d2314b4e97f2b
Author: Timm Bäder <mail baedert org>
Date:   Fri Feb 28 08:59:23 2020 +0100

    macros: Define G_GNUC_FALLTHROUGH for more compilers
    
    Some compilers have __GNUC__ defined as a value less than 6, but do
    support implicit-fallthrough via __attribute__((fallthrough)). Define
    G_GNUC_FALLTHROUGH for those that support __has_attribute.

 glib/gmacros.h | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/glib/gmacros.h b/glib/gmacros.h
index 1f4d779be..76be83fb4 100644
--- a/glib/gmacros.h
+++ b/glib/gmacros.h
@@ -559,6 +559,8 @@
  */
 #if    __GNUC__ > 6
 #define G_GNUC_FALLTHROUGH __attribute__((fallthrough))
+#elif g_macro__has_attribute (fallthrough)
+#define G_GNUC_FALLTHROUGH __attribute__((fallthrough))
 #else
 #define G_GNUC_FALLTHROUGH
 #endif /* __GNUC__ */