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

On case insensitive filesystems, "tags" and "TAGS" target will try to
overwrite the same file.  Allow MinGW to use "ETAGS" instead.

These two targets do produce real files; do not put them on .PHONY target
list.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -390,6 +390,8 @@ SCRIPTS = $(patsubst %.sh,%,$(SCRIPT_SH)) \
 	  $(patsubst %.py,%,$(SCRIPT_PYTHON)) \
 	  git-instaweb
 
+ETAGS_TARGET = TAGS
+
 # Empty...
 EXTRA_PROGRAMS =
 
@@ -1122,6 +1124,7 @@ ifneq (,$(findstring MINGW,$(uname_S)))
 	NO_REGEX = YesPlease
 	NO_PYTHON = YesPlease
 	BLK_SHA1 = YesPlease
+	ETAGS_TARGET = ETAGS
 	COMPAT_CFLAGS += -D__USE_MINGW_ACCESS -DNOGDI -Icompat -Icompat/fnmatch -Icompat/win32
 	COMPAT_CFLAGS += -DSTRIP_EXTENSION=\".exe\"
 	COMPAT_OBJS += compat/mingw.o compat/fnmatch/fnmatch.o compat/winansi.o \
@@ -1961,11 +1964,11 @@ info:
 pdf:
 	$(MAKE) -C Documentation pdf
 
-TAGS:
-	$(RM) TAGS
-	$(FIND) . -name '*.[hcS]' -print | xargs etags -a
+$(ETAGS_TARGET): FORCE
+	$(RM) $(ETAGS_TARGET)
+	$(FIND) . -name '*.[hcS]' -print | xargs etags -a -o $(ETAGS_TARGET)
 
-tags:
+tags: FORCE
 	$(RM) tags
 	$(FIND) . -name '*.[hcS]' -print | xargs ctags -a
 
@@ -2235,7 +2238,7 @@ clean:
 	$(RM) $(TEST_PROGRAMS)
 	$(RM) -r bin-wrappers
 	$(RM) -r $(dep_dirs)
-	$(RM) *.spec *.pyc *.pyo */*.pyc */*.pyo common-cmds.h TAGS tags cscope*
+	$(RM) *.spec *.pyc *.pyo */*.pyc */*.pyo common-cmds.h $(ETAGS_TARGET) tags cscope*
 	$(RM) -r autom4te.cache
 	$(RM) config.log config.mak.autogen config.mak.append config.status config.cache
 	$(RM) -r $(GIT_TARNAME) .doc-tmp-dir
@@ -2259,7 +2262,7 @@ endif
 
 .PHONY: all install clean strip
 .PHONY: shell_compatibility_test please_set_SHELL_PATH_to_a_more_modern_shell
-.PHONY: FORCE TAGS tags cscope
+.PHONY: FORCE cscope
 
 ### Check documentation
 #