compat: some mkdir() do not like a slash at the end

Introduce a compatibility helper for platforms with such a mkdir().

Signed-off-by: Joachim Schmitz <jojo@schmitz-digital.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-compat-util.h

@@ -162,6 +162,11 @@
 #define probe_utf8_pathname_composition(a,b)
 #endif
 
+#ifdef MKDIR_WO_TRAILING_SLASH
+#define mkdir(a,b) compat_mkdir_wo_trailing_slash((a),(b))
+extern int compat_mkdir_wo_trailing_slash(const char*, mode_t);
+#endif
+
 #ifndef NO_LIBGEN_H
 #include <libgen.h>
 #else