Pass on all CPPFLAGS that look like -I* to the PL/Perl build.

(This previously worked, but must have gotten lost somewhere...)

src/pl/plperl/GNUmakefile

-# $Header: /cvsroot/pgsql/src/pl/plperl/GNUmakefile,v 1.5 2000/10/24 17:01:05 tgl Exp $
+# $Header: /cvsroot/pgsql/src/pl/plperl/GNUmakefile,v 1.6 2000/11/02 18:40:13 petere Exp $
 
 subdir = src/pl/plperl
 top_builddir = ../../..
@@ -11,8 +11,8 @@ all: Makefile
 	$(MAKE) -f $< all
 
 Makefile: Makefile.PL
-	@plperl_installdir='$(plperl_installdir)' \
-	  EXTRA_INCLUDES='-I$(top_srcdir)/src/include $(INCLUDES)' \
+	plperl_installdir='$(plperl_installdir)' \
+	EXTRA_INCLUDES='$(filter -I%, $(CPPFLAGS))' \
 	$(PERL) $<
 
 install: all installdirs