Cygwin *might* be helped with NO_MMAP

When HPA added Cygwin target, it ran just fine without NO_MMAP for him,
but recently we are getting reports that for some people things break
without it.  For now, just suggest it in the Makefile without actually
updating the default.

Signed-off-by: Junio C Hamano <junkio@cox.net>

Makefile

@@ -208,6 +208,10 @@ endif
 ifeq ($(uname_O),Cygwin)
 	NO_STRCASESTR = YesPlease
 	NEEDS_LIBICONV = YesPlease
+	# There are conflicting reports about this.
+	# On some boxes NO_MMAP is needed, and not so elsewhere.
+	# Try uncommenting this if you see things break -- YMMV.
+	# NO_MMAP = YesPlease
 	NO_IPV6 = YesPlease
 	X = .exe
 	ALL_CFLAGS += -DUSE_SYMLINK_HEAD=0