Makefile: simplify by using SCRIPT_{PERL,SH}_GEN macros

SCRIPT_PERL_GEN is defined as $(patsubst %.perl,%,$(SCRIPT_PERL))
for use in targets like build-perl-script used by makefiles in
subdirectories that override SCRIPT_PERL (see v1.8.2-rc0~17^2,
"git-remote-mediawiki: use toplevel's Makefile", 2013-02-08).

The same expression is used in the rules that actually write the
generated perl scripts, and since these rules were introduced before
SCRIPT_PERL_GEN, they use the longhand instead of that macro.  Use the
macro to make reading easier.

Likewise for SCRIPT_SH_GEN.  The Python rules already got the same
simplification in v1.8.4-rc0~162^2~8 (2013-05-24).

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -1787,7 +1787,7 @@ GIT-SCRIPT-DEFINES: FORCE
             fi
 
 
-$(patsubst %.sh,%,$(SCRIPT_SH)) : % : %.sh GIT-SCRIPT-DEFINES
+$(SCRIPT_SH_GEN) : % : %.sh GIT-SCRIPT-DEFINES
 	$(QUIET_GEN)$(cmd_munge_script) && \
 	chmod +x $@+ && \
 	mv $@+ $@
@@ -1802,10 +1802,10 @@ git.res: git.rc GIT-VERSION-FILE
 	  -DGIT_VERSION="\\\"$(GIT_VERSION)\\\"" $< -o $@
 
 # This makes sure we depend on the NO_PERL setting itself.
-$(patsubst %.perl,%,$(SCRIPT_PERL)): GIT-BUILD-OPTIONS
+$(SCRIPT_PERL_GEN): GIT-BUILD-OPTIONS
 
 ifndef NO_PERL
-$(patsubst %.perl,%,$(SCRIPT_PERL)): perl/perl.mak
+$(SCRIPT_PERL_GEN): perl/perl.mak
 
 perl/perl.mak: perl/PM.stamp
 
@@ -1818,7 +1818,7 @@ 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)
 
 PERL_DEFINES = $(PERL_PATH_SQ):$(PERLLIB_EXTRA_SQ)
-$(patsubst %.perl,%,$(SCRIPT_PERL)): % : %.perl perl/perl.mak GIT-PERL-DEFINES GIT-VERSION-FILE
+$(SCRIPT_PERL_GEN): % : %.perl perl/perl.mak GIT-PERL-DEFINES GIT-VERSION-FILE
 	$(QUIET_GEN)$(RM) $@ $@+ && \
 	INSTLIBDIR=`MAKEFLAGS= $(MAKE) -C perl -s --no-print-directory instlibdir` && \
 	INSTLIBDIR_EXTRA='$(PERLLIB_EXTRA_SQ)' && \
@@ -1852,7 +1852,7 @@ git-instaweb: git-instaweb.sh gitweb GIT-SCRIPT-DEFINES
 	chmod +x $@+ && \
 	mv $@+ $@
 else # NO_PERL
-$(patsubst %.perl,%,$(SCRIPT_PERL)) git-instaweb: % : unimplemented.sh
+$(SCRIPT_PERL_GEN) git-instaweb: % : unimplemented.sh
 	$(QUIET_GEN)$(RM) $@ $@+ && \
 	sed -e '1s|#!.*/sh|#!$(SHELL_PATH_SQ)|' \
 	    -e 's|@@REASON@@|NO_PERL=$(NO_PERL)|g' \