msvc: avoid collisions between "tags" and "TAGS"

Commit 2f76919 ("MinGW: avoid collisions between "tags" and "TAGS",
28-09-2010) enabled MinGW to use an ETAGS file in order to avoid
filename collisions on (Windows) case insensitive filesystems. In
addition, this prevents 'make' from issuing several warning messages.

When using the Makefile to perform an MSVC build, which is usually
executed using MinGW tools, we can also benefit from this capability.
In order to reap the above benefits, we set the ETAGS_TARGET build
variable to ETAGS in the MSVC config block.

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Tested-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.mak.uname

@@ -343,6 +343,7 @@ ifeq ($(uname_S),Windows)
 	NO_CURL = YesPlease
 	NO_PYTHON = YesPlease
 	BLK_SHA1 = YesPlease
+	ETAGS_TARGET = ETAGS
 	NO_INET_PTON = YesPlease
 	NO_INET_NTOP = YesPlease
 	NO_POSIX_GOODIES = UnfortunatelyYes