Really fix headers for __FreeBSD__

The symbol to detect FreeBSD is __FreeBSD__, not __FreeBSD.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

git-compat-util.h

@@ -11,7 +11,7 @@
 
 #define ARRAY_SIZE(x) (sizeof(x)/sizeof(x[0]))
 
-#if !defined(__APPLE__) && !defined(__FreeBSD)
+#if !defined(__APPLE__) && !defined(__FreeBSD__)
 #define _XOPEN_SOURCE 600 /* glibc2 and AIX 5.3L need 500, OpenBSD needs 600 for S_ISLNK() */
 #define _XOPEN_SOURCE_EXTENDED 1 /* AIX 5.3L needs this */
 #endif