While experimenting with cross-building by specifying just TARGET,

I found one bug.  Pass our idea of TARGET_ARCH and TARGET down to
XMAKE, the cross-tools make.  Previously it worked because usually
TARGET_ARCH was specified on the initial make's command line.
This should also allow us to simplify the "universe" target, which
I'm currently testing.

Makefile.inc1

@@ -212,6 +212,7 @@ TMAKE=		MAKEOBJDIRPREFIX=${OBJTREE} \
 
 # cross-tools stage
 XMAKE=		TOOLS_PREFIX=${WORLDTMP} ${BMAKE} \
+		TARGET=${TARGET} TARGET_ARCH=${TARGET_ARCH} \
 		-DWITHOUT_FORTRAN -DWITHOUT_GDB
 
 # world stage