Properly define HAS_PERL6

Makefile

@@ -35,15 +35,15 @@ PARROT_IS_INSECURE = $(shell expr $(PARROTREVISION) \< $(MINPARROTREVISION))
 # PGVER_MINOR = $(shell echo $(VERSION) | awk -F. '{ print ($$2 + 0) }')
 # PGVER_PATCH = $(shell echo $(VERSION) | awk -F. '{ print ($$3 + 0) }')
 
+
 override CPPFLAGS := -I$(PARROTINC) -I$(srcdir) $(CPPFLAGS)
 override CFLAGS   := $(PARROTLDFLAGS) $(PARROTLINKFLAGS) $(CFLAGS)
 
-ifdef ($(PERL6PBC))
-override CFLAGS := $(CFLAGS) -DHAS_PERL6 -D'PERL6PBC="$(PERL6PBC)"'
-endif
-
 # It would be nice if this ran before we compiled
 all: check_revision headers
+ifneq ($(PERL6PBC),)
+override CFLAGS := $(CFLAGS) -DHAS_PERL6 -D'PERL6PBC="$(PERL6PBC)"'
+endif
 	@echo "\n\n\tHappy Hacking with PL/Parrot!\n\n"
 
 headers:

plparrot.c

@@ -117,7 +117,7 @@ _PG_init(void)
     trusted_interp = Parrot_new(untrusted_interp);
 
     //Parrot_set_trace(interp, PARROT_ALL_TRACE_FLAGS);
-#if HAS_PERL6
+#ifdef HAS_PERL6
     p6_interp = Parrot_new(trusted_interp);
     p6u_interp = Parrot_new(untrusted_interp);
     if (!p6_interp) {