Fix some -Wpedantic warning

Fixes
ISO C does not support ‘__FUNCTION__’ predefined identifier

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Gert Wollny <gert.wollny@collabora.com>

vtest/util.h

@@ -32,9 +32,9 @@ int __failed_call(const char* func, const char *called, int ret);
 int __failure(const char* func, const char *reason, int ret);
 
 #define report_failure(reason, ret) \
-   __failure(__FUNCTION__, reason, ret)
+   __failure(__func__, reason, ret)
 
 #define report_failed_call(called, ret) \
-   __failed_call(__FUNCTION__, called, ret)
+   __failed_call(__func__, called, ret)
 
 #endif /* VTEST_UTIL_H */