Fix xorg-server under ia64 and powerpc

[Julio Merino]

Hello,

The xorg-server has obvious problems when building in ia64 and powerpc64
because it overrides EXTRA_PATCHES half-way through the Makefile and thus
clears previously-set values.

In particular, I'm seeing build failures in powerpc64 when enabling devd
because the devd.c file patch is not being applied as it should be.

OK to commit patch below?  (Please provide your explicit approval.)

Thanks.

Index: Makefile
===================================================================
--- Makefile	(revision 349914)
+++ Makefile	(working copy)
@@ -124,7 +124,7 @@
 
 .if ${ARCH} == ia64
 PLIST_SUB+=	IA64_NA="@comment "
-EXTRA_PATCHES=	${.CURDIR}/files/extra-arch-ia64
+EXTRA_PATCHES+=	${.CURDIR}/files/extra-arch-ia64
 .else
 PLIST_SUB+=	IA64_NA=""
 .endif
@@ -132,9 +132,9 @@
 .if ${ARCH} == powerpc || ${ARCH} == powerpc64
 PLIST_SUB+=	PPC_NA="@comment "
 .if defined(WITH_NEW_XORG)
-EXTRA_PATCHES=	${.CURDIR}/files/extra-new-arch-powerpc
+EXTRA_PATCHES+=	${.CURDIR}/files/extra-new-arch-powerpc
 .else
-EXTRA_PATCHES=	${.CURDIR}/files/extra-old-arch-powerpc
+EXTRA_PATCHES+=	${.CURDIR}/files/extra-old-arch-powerpc
 .endif
 .else
 PLIST_SUB+=	PPC_NA=""