Merge branch 'cb/reftable-unused-portability-fix'

Build fix.

* cb/reftable-unused-portability-fix:
  reftable: make REFTABLE_UNUSED C99 compatible

Author: gitster

reftable/basics.h

@@ -16,7 +16,11 @@
 #include "system.h"
 #include "reftable-basics.h"
 
+#ifdef __GNUC__
 #define REFTABLE_UNUSED __attribute__((__unused__))
+#else
+#define REFTABLE_UNUSED
+#endif
 
 /*
  * Initialize the buffer such that it is ready for use. This is equivalent to