Make hstore_plperl's build even more like plperl's

Combine the two places that set CPPFLAGS into one.  Also, some settings
should be restricted to Windows only.  More precisely, -Wno-comment is
a GCC-only option, but Windows in a makefile implies GCC at the moment.

Also, since -Wno-comment is more properly a preprocessor option, move it
to CPPFLAGS to simplify things a bit.

contrib/hstore_plperl/Makefile

@@ -3,7 +3,12 @@
 MODULE_big = hstore_plperl
 OBJS = hstore_plperl.o
 
-PG_CPPFLAGS = -I$(top_srcdir)/src/pl/plperl -I$(top_srcdir)/contrib/hstore
+PG_CPPFLAGS = -I$(top_srcdir)/src/pl/plperl -I$(top_srcdir)/contrib/hstore -I$(perl_archlibexp)/CORE
+
+# see plperl
+ifeq ($(PORTNAME), win32)
+PG_CPPFLAGS += -DPLPERL_HAVE_UID_GID -Wno-comment
+endif
 
 EXTENSION = hstore_plperl hstore_plperlu
 DATA = hstore_plperl--1.0.sql hstore_plperlu--1.0.sql
@@ -21,6 +26,3 @@ top_builddir = ../..
 include $(top_builddir)/src/Makefile.global
 include $(top_srcdir)/contrib/contrib-global.mk
 endif
-
-override CPPFLAGS := $(CPPFLAGS) -I$(perl_archlibexp)/CORE -DPLPERL_HAVE_UID_GID
-override CFLAGS += -Wno-comment

src/pl/plperl/GNUmakefile

@@ -9,7 +9,7 @@ ifeq ($(PORTNAME), win32)
 override CPPFLAGS += -DPLPERL_HAVE_UID_GID
 # Perl on win32 contains /* within comment all over the header file,
 # so disable this warning.
-override CFLAGS += -Wno-comment
+override CPPFLAGS += -Wno-comment
 endif
 
 override CPPFLAGS := -I. -I$(srcdir) $(CPPFLAGS) -I$(perl_archlibexp)/CORE