git-compat-util.h: Support variadic macros with the XL C compiler

When the XL C compiler is run with an appropriate language level or suboption, it defines a feature test macro to indicate support for variadic macros.

This was tested on z/OS, but it should also work on AIX according to IBM documentation.

---
 git-compat-util.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 2107127..b31cfdd 100644
@@ -778,7 +778,7 @@ void git_qsort(void *base, size_t nmemb, size_t size,
 #endif
 #endif
 
-#if defined(__GNUC__) || (_MSC_VER >= 1400)
+#if defined(__GNUC__) || (_MSC_VER >= 1400) || defined(__C99_MACRO_WITH_VA_ARGS)
 #define HAVE_VARIADIC_MACROS 1
 #endif
 

1.9.3