Avoid C99 comments, use old-style C comments instead.

This doesn't make the code uglier or harder to read, yet it makes the
code more portable.  This also simplifies checking for other potential
incompatibilities.  "gcc -std=c89 -pedantic" can flag many incompatible
constructs as warnings, but C99 comments will cause it to emit an error.

Signed-off-by: Pavel Roskin <proski@gnu.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

read-cache.c

@@ -748,7 +748,7 @@ int read_cache(void)
 		die("index file open failed (%s)", strerror(errno));
 	}
 
-	size = 0; // avoid gcc warning
+	size = 0; /* avoid gcc warning */
 	map = MAP_FAILED;
 	if (!fstat(fd, &st)) {
 		size = st.st_size;