Add a pre-fetch target to check CFLAGS. XFree won't compile with -O3 or above

with xthreads.
Bump PORTREVISION.

x11/XFree86-4/Makefile

@@ -7,7 +7,7 @@
 
 PORTNAME=	XFree86
 PORTVERSION=	4.0.2
-PORTREVISION=	5
+PORTREVISION=	6
 CATEGORIES=	x11
 MASTER_SITES=	${MASTER_SITE_XFREE}
 MASTER_SITE_SUBDIR=	${PORTVERSION}
@@ -51,6 +51,12 @@ SCRIPTS_ENV+=	MACHINE=alpha
 PLIST=		${PKGDIR}/pkg-plist.alpha
 .endif
 
+pre-fetch:
+	@if ${ECHO} "$(CFLAGS)" |${GREP} -q O[3456789]; then \
+		${ECHO} "XFree86-4 with thread support does not build with optimization"; \
+		${ECHO} "flags different from O or -O2"; \
+		${FALSE}; fi
+
 .if defined(XDM_DES) && (${USA_RESIDENT} != YES && ${USA_RESIDENT} != NO)
 pre-fetch:
 	@${ECHO}