Makefile: extract script to massage Perl scripts

Extract the script to inject various build-time parameters into our Perl
scripts into a standalone script. This is done such that we can reuse it
in other build systems.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -2606,16 +2606,8 @@ endif
 
 PERL_DEFINES += $(gitexecdir) $(perllibdir) $(localedir)
 
-$(SCRIPT_PERL_GEN): % : %.perl GIT-PERL-DEFINES GIT-PERL-HEADER GIT-VERSION-FILE
-	$(QUIET_GEN) \
-	sed -e '1{' \
-	    -e '	s|#!.*perl|#!$(PERL_PATH_SQ)|' \
-	    -e '	r GIT-PERL-HEADER' \
-	    -e '	G' \
-	    -e '}' \
-	    -e 's/@GIT_VERSION@/$(GIT_VERSION)/g' \
-	    $< >$@+ && \
-	chmod +x $@+ && \
+$(SCRIPT_PERL_GEN): % : %.perl generate-perl.sh GIT-PERL-DEFINES GIT-PERL-HEADER GIT-VERSION-FILE
+	$(QUIET_GEN)$(SHELL_PATH) generate-perl.sh ./GIT-BUILD-OPTIONS ./GIT-VERSION-FILE GIT-PERL-HEADER "$<" "$@+" && \
 	mv $@+ $@
 
 PERL_DEFINES := $(subst $(space),:,$(PERL_DEFINES))