Makefile: rebuild perl scripts when perl paths change

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

.gitignore

@@ -2,6 +2,7 @@
 /GIT-CFLAGS
 /GIT-LDFLAGS
 /GIT-PREFIX
+/GIT-PERL-DEFINES
 /GIT-PYTHON-VARS
 /GIT-SCRIPT-DEFINES
 /GIT-USER-AGENT

Makefile

@@ -1792,7 +1792,8 @@ perl/PM.stamp: FORCE
 perl/perl.mak: GIT-CFLAGS GIT-PREFIX perl/Makefile perl/Makefile.PL
 	$(QUIET_SUBDIR0)perl $(QUIET_SUBDIR1) PERL_PATH='$(PERL_PATH_SQ)' prefix='$(prefix_SQ)' $(@F)
 
-$(patsubst %.perl,%,$(SCRIPT_PERL)): % : %.perl GIT-VERSION-FILE
+PERL_DEFINES = $(PERL_PATH_SQ)
+$(patsubst %.perl,%,$(SCRIPT_PERL)): % : %.perl perl/perl.mak GIT-PERL-DEFINES GIT-VERSION-FILE
 	$(QUIET_GEN)$(RM) $@ $@+ && \
 	INSTLIBDIR=`MAKEFLAGS= $(MAKE) -C perl -s --no-print-directory instlibdir` && \
 	sed -e '1{' \
@@ -1807,6 +1808,13 @@ $(patsubst %.perl,%,$(SCRIPT_PERL)): % : %.perl GIT-VERSION-FILE
 	chmod +x $@+ && \
 	mv $@+ $@
 
+GIT-PERL-DEFINES: FORCE
+	@FLAGS='$(PERL_DEFINES)'; \
+	    if test x"$$FLAGS" != x"`cat $@ 2>/dev/null`" ; then \
+		echo >&2 "    * new perl-specific parameters"; \
+		echo "$$FLAGS" >$@; \
+	    fi
+
 
 .PHONY: gitweb
 gitweb:
@@ -2494,7 +2502,8 @@ ifndef NO_TCLTK
 	$(MAKE) -C git-gui clean
 endif
 	$(RM) GIT-VERSION-FILE GIT-CFLAGS GIT-LDFLAGS GIT-BUILD-OPTIONS
-	$(RM) GIT-USER-AGENT GIT-PREFIX GIT-SCRIPT-DEFINES GIT-PYTHON-VARS
+	$(RM) GIT-USER-AGENT GIT-PREFIX
+	$(RM) GIT-SCRIPT-DEFINES GIT-PERL-DEFINES GIT-PYTHON-VARS
 
 .PHONY: all install profile-clean clean strip
 .PHONY: shell_compatibility_test please_set_SHELL_PATH_to_a_more_modern_shell