Propagate with_system_tzdata setting into initdb build.

findtimezone.c needs to know this setting too.  Per Peter Eisentraut.

src/bin/initdb/Makefile

@@ -18,6 +18,11 @@ include $(top_builddir)/src/Makefile.global
 
 override CPPFLAGS := -DFRONTEND -I$(libpq_srcdir) -I$(top_srcdir)/src/timezone $(CPPFLAGS)
 
+# use system timezone data?
+ifneq (,$(with_system_tzdata))
+override CPPFLAGS += '-DSYSTEMTZDIR="$(with_system_tzdata)"'
+endif
+
 OBJS=	initdb.o findtimezone.o localtime.o encnames.o pqsignal.o $(WIN32RES)
 
 all: initdb