Makefile: avoid timestamp updates to GIT-BUILD-OPTIONS

We force the GIT-BUILD-OPTIONS recipe to run every time
"make" is invoked. We must do this to catch new options
which may have come from the command-line or environment.

However, we actually update the file's timestamp each time
the recipe is run, whether anything changed or not. As a
result, any files which depend on it (for example, all of
the perl scripts, which need to know whether NO_PERL was
set) will be re-built every time.

Let's do our usual trick of writing to a tempfile, then
doing a "cmp || mv" to update the file only when something
changed.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -2041,45 +2041,46 @@ GIT-LDFLAGS: FORCE
 # that runs GIT-BUILD-OPTIONS, and then again to protect it
 # and the first level quoting from the shell that runs "echo".
 GIT-BUILD-OPTIONS: FORCE
-	@echo SHELL_PATH=\''$(subst ','\'',$(SHELL_PATH_SQ))'\' >$@
-	@echo PERL_PATH=\''$(subst ','\'',$(PERL_PATH_SQ))'\' >>$@
-	@echo DIFF=\''$(subst ','\'',$(subst ','\'',$(DIFF)))'\' >>$@
-	@echo PYTHON_PATH=\''$(subst ','\'',$(PYTHON_PATH_SQ))'\' >>$@
-	@echo TAR=\''$(subst ','\'',$(subst ','\'',$(TAR)))'\' >>$@
-	@echo NO_CURL=\''$(subst ','\'',$(subst ','\'',$(NO_CURL)))'\' >>$@
-	@echo USE_LIBPCRE=\''$(subst ','\'',$(subst ','\'',$(USE_LIBPCRE)))'\' >>$@
-	@echo NO_PERL=\''$(subst ','\'',$(subst ','\'',$(NO_PERL)))'\' >>$@
-	@echo NO_PYTHON=\''$(subst ','\'',$(subst ','\'',$(NO_PYTHON)))'\' >>$@
-	@echo NO_UNIX_SOCKETS=\''$(subst ','\'',$(subst ','\'',$(NO_UNIX_SOCKETS)))'\' >>$@
+	@echo SHELL_PATH=\''$(subst ','\'',$(SHELL_PATH_SQ))'\' >$@+
+	@echo PERL_PATH=\''$(subst ','\'',$(PERL_PATH_SQ))'\' >>$@+
+	@echo DIFF=\''$(subst ','\'',$(subst ','\'',$(DIFF)))'\' >>$@+
+	@echo PYTHON_PATH=\''$(subst ','\'',$(PYTHON_PATH_SQ))'\' >>$@+
+	@echo TAR=\''$(subst ','\'',$(subst ','\'',$(TAR)))'\' >>$@+
+	@echo NO_CURL=\''$(subst ','\'',$(subst ','\'',$(NO_CURL)))'\' >>$@+
+	@echo USE_LIBPCRE=\''$(subst ','\'',$(subst ','\'',$(USE_LIBPCRE)))'\' >>$@+
+	@echo NO_PERL=\''$(subst ','\'',$(subst ','\'',$(NO_PERL)))'\' >>$@+
+	@echo NO_PYTHON=\''$(subst ','\'',$(subst ','\'',$(NO_PYTHON)))'\' >>$@+
+	@echo NO_UNIX_SOCKETS=\''$(subst ','\'',$(subst ','\'',$(NO_UNIX_SOCKETS)))'\' >>$@+
 ifdef TEST_OUTPUT_DIRECTORY
-	@echo TEST_OUTPUT_DIRECTORY=\''$(subst ','\'',$(subst ','\'',$(TEST_OUTPUT_DIRECTORY)))'\' >>$@
+	@echo TEST_OUTPUT_DIRECTORY=\''$(subst ','\'',$(subst ','\'',$(TEST_OUTPUT_DIRECTORY)))'\' >>$@+
 endif
 ifdef GIT_TEST_OPTS
-	@echo GIT_TEST_OPTS=\''$(subst ','\'',$(subst ','\'',$(GIT_TEST_OPTS)))'\' >>$@
+	@echo GIT_TEST_OPTS=\''$(subst ','\'',$(subst ','\'',$(GIT_TEST_OPTS)))'\' >>$@+
 endif
 ifdef GIT_TEST_CMP
-	@echo GIT_TEST_CMP=\''$(subst ','\'',$(subst ','\'',$(GIT_TEST_CMP)))'\' >>$@
+	@echo GIT_TEST_CMP=\''$(subst ','\'',$(subst ','\'',$(GIT_TEST_CMP)))'\' >>$@+
 endif
 ifdef GIT_TEST_CMP_USE_COPIED_CONTEXT
-	@echo GIT_TEST_CMP_USE_COPIED_CONTEXT=YesPlease >>$@
+	@echo GIT_TEST_CMP_USE_COPIED_CONTEXT=YesPlease >>$@+
 endif
-	@echo NO_GETTEXT=\''$(subst ','\'',$(subst ','\'',$(NO_GETTEXT)))'\' >>$@
-	@echo GETTEXT_POISON=\''$(subst ','\'',$(subst ','\'',$(GETTEXT_POISON)))'\' >>$@
+	@echo NO_GETTEXT=\''$(subst ','\'',$(subst ','\'',$(NO_GETTEXT)))'\' >>$@+
+	@echo GETTEXT_POISON=\''$(subst ','\'',$(subst ','\'',$(GETTEXT_POISON)))'\' >>$@+
 ifdef GIT_PERF_REPEAT_COUNT
-	@echo GIT_PERF_REPEAT_COUNT=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_REPEAT_COUNT)))'\' >>$@
+	@echo GIT_PERF_REPEAT_COUNT=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_REPEAT_COUNT)))'\' >>$@+
 endif
 ifdef GIT_PERF_REPO
-	@echo GIT_PERF_REPO=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_REPO)))'\' >>$@
+	@echo GIT_PERF_REPO=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_REPO)))'\' >>$@+
 endif
 ifdef GIT_PERF_LARGE_REPO
-	@echo GIT_PERF_LARGE_REPO=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_LARGE_REPO)))'\' >>$@
+	@echo GIT_PERF_LARGE_REPO=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_LARGE_REPO)))'\' >>$@+
 endif
 ifdef GIT_PERF_MAKE_OPTS
-	@echo GIT_PERF_MAKE_OPTS=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_MAKE_OPTS)))'\' >>$@
+	@echo GIT_PERF_MAKE_OPTS=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_MAKE_OPTS)))'\' >>$@+
 endif
 ifdef TEST_GIT_INDEX_VERSION
-	@echo TEST_GIT_INDEX_VERSION=\''$(subst ','\'',$(subst ','\'',$(TEST_GIT_INDEX_VERSION)))'\' >>$@
+	@echo TEST_GIT_INDEX_VERSION=\''$(subst ','\'',$(subst ','\'',$(TEST_GIT_INDEX_VERSION)))'\' >>$@+
 endif
+	@if cmp $@+ $@ >/dev/null 2>&1; then $(RM) $@+; else mv $@+ $@; fi
 
 ### Detect Python interpreter path changes
 ifndef NO_PYTHON