Index: head/Makefile
===================================================================
--- head/Makefile
+++ head/Makefile
@@ -513,14 +513,20 @@
 TARGET_ARCHES_${target}?= ${target}
 .endfor
 
-# Remove architectures only supported by external toolchain from
-# universe if required toolchain packages are missing.
-# Note: We no longer have targets that require an external toolchain, but for
-# now keep this block in case a new non-LLVM architecture is added and to reuse
-# it for a future extenal GCC make universe variant.
-_external_toolchain_targets=
-.for target in ${_external_toolchain_targets}
-.if ${_UNIVERSE_TARGETS:M${target}}
+.if defined(USE_GCC_TOOLCHAINS)
+TOOLCHAINS_amd64=	amd64-gcc6
+TOOLCHAINS_arm64=	aarch64-gcc6
+TOOLCHAINS_i386=	i386-gcc6
+TOOLCHAINS_mips=	mips-gcc6
+TOOLCHAINS_powerpc=	powerpc-gcc6 powerpc64-gcc6
+TOOLCHAIN_powerpc64=	powerpc64-gcc6
+.endif
+
+# If a target is using an external toolchain, set MAKE_PARAMS to enable use
+# of the toolchain.  If the external toolchain is missing, exclude the target
+# from universe.
+.for target in ${_UNIVERSE_TARGETS}
+.if !empty(TOOLCHAINS_${target})
 .for toolchain in ${TOOLCHAINS_${target}}
 .if !exists(/usr/local/share/toolchains/${toolchain}.mk)
 _UNIVERSE_TARGETS:= ${_UNIVERSE_TARGETS:N${target}}
@@ -530,6 +536,10 @@
 	@echo ">> ${target} skipped - install ${toolchain} port or package to build"
 .endif
 .endfor
+.for arch in ${TARGET_ARCHES_${target}}
+TOOLCHAIN_${arch}?=	${TOOLCHAINS_${target}:[1]}
+MAKE_PARAMS_${arch}?=	CROSS_TOOLCHAIN=${TOOLCHAIN_${arch}}
+.endfor
 .endif
 .endfor
 
@@ -604,7 +614,7 @@
 _need_clang_${target}_${target_arch} != \
 	env TARGET=${target} TARGET_ARCH=${target_arch} \
 	${SUB_MAKE} -C ${.CURDIR} -f Makefile.inc1 test-system-compiler \
-	    ${MAKE_PARAMS_${target}} -V MK_CLANG_BOOTSTRAP 2>/dev/null || \
+	    ${MAKE_PARAMS_${target_arch}} -V MK_CLANG_BOOTSTRAP 2>/dev/null || \
 	    echo unknown
 .export _need_clang_${target}_${target_arch}
 .endif
@@ -612,7 +622,7 @@
 _need_lld_${target}_${target_arch} != \
 	env TARGET=${target} TARGET_ARCH=${target_arch} \
 	${SUB_MAKE} -C ${.CURDIR} -f Makefile.inc1 test-system-linker \
-	    ${MAKE_PARAMS_${target}} -V MK_LLD_BOOTSTRAP 2>/dev/null || \
+	    ${MAKE_PARAMS_${target_arch}} -V MK_LLD_BOOTSTRAP 2>/dev/null || \
 	    echo unknown
 .export _need_lld_${target}_${target_arch}
 .endif
@@ -628,7 +638,7 @@
 #      supports all TARGETS though.
 # For now we only pass UNIVERSE_TOOLCHAIN_PATH which will be added at the end
 # of STRICTTMPPATH to ensure that the target-specific binaries come first.
-MAKE_PARAMS_${target}+= \
+MAKE_PARAMS_${target_arch}+= \
 	XCC="${HOST_OBJTOP}/tmp/usr/bin/cc" \
 	XCXX="${HOST_OBJTOP}/tmp/usr/bin/c++" \
 	XCPP="${HOST_OBJTOP}/tmp/usr/bin/cpp" \
@@ -636,7 +646,7 @@
 .endif
 .if defined(_need_lld_${target}_${target_arch}) && \
     ${_need_lld_${target}_${target_arch}} == "yes"
-MAKE_PARAMS_${target}+= \
+MAKE_PARAMS_${target_arch}+= \
 	XLD="${HOST_OBJTOP}/tmp/usr/bin/ld"
 .endif
 .endfor
@@ -659,7 +669,7 @@
 	    ${SUB_MAKE} ${JFLAG} ${UNIVERSE_TARGET} \
 	    TARGET=${target} \
 	    TARGET_ARCH=${target_arch} \
-	    ${MAKE_PARAMS_${target}} \
+	    ${MAKE_PARAMS_${target_arch}} \
 	    > _.${target}.${target_arch}.${UNIVERSE_TARGET} 2>&1 || \
 	    (echo "${target}.${target_arch} ${UNIVERSE_TARGET} failed," \
 	    "check _.${target}.${target_arch}.${UNIVERSE_TARGET} for details" | \
@@ -724,7 +734,7 @@
 	    ${SUB_MAKE} ${JFLAG} buildkernel \
 	    TARGET=${TARGET} \
 	    TARGET_ARCH=${TARGET_ARCH_${kernel}} \
-	    ${MAKE_PARAMS_${TARGET}} \
+	    ${MAKE_PARAMS_${TARGET_ARCH}} \
 	    KERNCONF=${kernel} \
 	    > _.${TARGET}.${kernel} 2>&1 || \
 	    (echo "${TARGET} ${kernel} kernel failed," \