Makefile: quote $INSTLIBDIR when passing it to sed

f6a0ad4 (Makefile: generate Perl header from template file,
2018-04-10) moved code for generating the 'use lib' lines at the top
of perl scripts from the $(SCRIPT_PERL_GEN) rule to a separate
GIT-PERL-HEADER rule.

This rule first populates INSTLIBDIR and then substitutes it into the
GIT-PERL-HEADER using sed:

	INSTLIBDIR=... something ...
	sed -e 's=@@INSTLIBDIR@@='$$INSTLIBDIR'=g' $< > $@

Because $INSTLIBDIR is not surrounded by double quotes, the shell
splits it at each space, causing errors if INSTLIBDIR contains an $IFS
character:

 sed: 1: "s=@@INSTLIBDIR@@=/usr/l ...": unescaped newline inside substitute pattern

Add back the missing double-quotes to make it work again.

Signed-off-by: Jonathan Nieder <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: jrn

Makefile

@@ -2098,7 +2098,7 @@ GIT-PERL-HEADER: $(PERL_HEADER_TEMPLATE) GIT-PERL-DEFINES Makefile
 	INSTLIBDIR_EXTRA='$(PERLLIB_EXTRA_SQ)' && \
 	INSTLIBDIR="$$INSTLIBDIR$${INSTLIBDIR_EXTRA:+:$$INSTLIBDIR_EXTRA}" && \
 	sed -e 's=@@PATHSEP@@=$(pathsep)=g' \
-	    -e 's=@@INSTLIBDIR@@='$$INSTLIBDIR'=g' \
+	    -e "s=@@INSTLIBDIR@@=$$INSTLIBDIR=g" \
 	    -e 's=@@PERLLIBDIR_REL@@=$(perllibdir_relative_SQ)=g' \
 	    -e 's=@@GITEXECDIR_REL@@=$(gitexecdir_relative_SQ)=g' \
 	    -e 's=@@LOCALEDIR_REL@@=$(localedir_relative_SQ)=g' \