Rather than using an extra variable, only call uname if really needed and

then directly assign the result.

Submitted by:	jmallett
MFC after:	24 days
X-MFC with:	r201815

Makefile

@@ -321,8 +321,9 @@ universe_${target}:
 	@echo ">> ${target} completed on `LC_ALL=C date`"
 .endfor
 universe_kernels: universe_kernconfs
-XMACHINE!=	uname -m
-TARGET?=	${XMACHINE}
+.if !defined(TARGET)
+TARGET!=	uname -m
+.endif
 KERNCONFS!=	cd ${.CURDIR}/sys/${TARGET}/conf && \
 		find [A-Z0-9]*[A-Z0-9] -type f -maxdepth 0 \
 		! -name DEFAULTS ! -name NOTES