Libcompat: Set build tools in environment rather than make overrides.

This allows the CXX hack in r300917 for external GCC to work for
the lib32 build.  It is also the same pattern as the native
build uses by adding the tools into CROSSENV for external
toolchain, rather than make overrides.

Sponsored by:	EMC / Isilon Storage Division

Makefile.libcompat

@@ -17,7 +17,7 @@ LIB32CPUFLAGS=	-march=${TARGET_CPUTYPE}
 .endif
 LIB32WMAKEENV=	MACHINE=i386 MACHINE_ARCH=i386 \
 		MACHINE_CPU="i686 mmx sse sse2"
-LIB32WMAKEFLAGS=	\
+LIB32WMAKEENV+=	\
 		AS="${XAS} --32" \
 		LD="${XLD} -m elf_i386_fbsd -Y P,${LIBCOMPATTMP}/usr/lib32" \
 		OBJCOPY="${XOBJCOPY}"
@@ -29,7 +29,7 @@ LIB32CPUFLAGS=	-mcpu=powerpc
 LIB32CPUFLAGS=	-mcpu=${TARGET_CPUTYPE}
 .endif
 LIB32WMAKEENV=	MACHINE=powerpc MACHINE_ARCH=powerpc
-LIB32WMAKEFLAGS=	\
+LIB32WMAKEENV+=	\
 		LD="${XLD} -m elf32ppc_fbsd" \
 		OBJCOPY="${XOBJCOPY}"
 .endif
@@ -84,9 +84,11 @@ LIBCOMPATWMAKEENV+= MAKEOBJDIRPREFIX=${LIBCOMPAT_OBJTREE} \
 # Don't rebuild build-tools targets during normal build.
 LIBCOMPATWMAKEENV+=	BUILD_TOOLS_META=.NOMETA_CMP
 .endif
-LIBCOMPATWMAKEFLAGS+= CC="${XCC} ${LIBCOMPATCFLAGS}" \
+LIBCOMPATWMAKEENV+= \
+		CC="${XCC} ${LIBCOMPATCFLAGS}" \
 		CXX="${XCXX} ${LIBCOMPATCFLAGS} ${LIBCOMPATCXXFLAGS}" \
-		CPP="${XCPP} ${LIBCOMPATCFLAGS}" \
+		CPP="${XCPP} ${LIBCOMPATCFLAGS}"
+LIBCOMPATWMAKEFLAGS+= \
 		DESTDIR=${LIBCOMPATTMP} \
 		-DNO_CPU_CFLAGS \
 		MK_CTF=no \