commit-slabs: move MAYBE_UNUSED out

after 36da893 ("config.mak.dev: enable -Wunused-function", 2018-10-18)
it is expected to be used to prevent -Wunused-function warnings for code
that was macro generated

Signed-off-by: Carlo Marcelo Arenas Belón <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: carenas

commit-slab-impl.h

@@ -1,10 +1,10 @@
 #ifndef COMMIT_SLAB_IMPL_H
 #define COMMIT_SLAB_IMPL_H
 
-#define MAYBE_UNUSED __attribute__((__unused__))
+#include "git-compat-util.h"
 
 #define implement_static_commit_slab(slabname, elemtype) \
-	implement_commit_slab(slabname, elemtype, static MAYBE_UNUSED)
+	implement_commit_slab(slabname, elemtype, MAYBE_UNUSED static)
 
 #define implement_shared_commit_slab(slabname, elemtype) \
 	implement_commit_slab(slabname, elemtype, )

git-compat-util.h

@@ -408,6 +408,8 @@ static inline char *git_find_last_dir_sep(const char *path)
 #define LAST_ARG_MUST_BE_NULL
 #endif
 
+#define MAYBE_UNUSED __attribute__((__unused__))
+
 #include "compat/bswap.h"
 
 #include "wildmatch.h"