Handle arm/armv[67] hosted/targeted builds gracefully

CPUTYPE (apparently) isn't defined in non-cross-builds, which caused
arm/armv[67] hosted/targeted builds to fail when evaluating CPUTYPE.

Add the :U modifier to CPUTYPE so it evaluates to "". This allows armv[67] to
get past the conditional successfully.

MFC after:	1 week
Reported by:	bob prohaska <fbsd@www.zefox.net>

lib/libclang_rt/Makefile.inc

@@ -3,7 +3,7 @@
 .include <bsd.compiler.mk>
 
 .if ${MACHINE} == "arm"
-.if ${MACHINE_ARCH:Marmv[67]*} != "" && ${CPUTYPE:M*soft*} == ""
+.if ${MACHINE_ARCH:Marmv[67]*} != "" && ${CPUTYPE:U:M*soft*} == ""
 CRTARCH=	armhf
 .endif
 .endif