build: use a different .toolchain-* file for each toolchian.

Makefile

@@ -60,11 +60,13 @@ distclean: clean
 		MAKELEVEL='' make clean ; \
 		MAKELEVEL='' make distclean ; \
 	fi
-	@${RM} -f .toolchain
+	@${RM} -f .toolchain-$(MCU_CORE)
 	$(Q)${RM} -f tags TAGS
 
 # Toolchain
-.toolchain:
+.toolchain: .toolchain-$(MCU_CORE)
+
+.toolchain-$(MCU_CORE):
 	$(Q)if [ ! -x ${CROSS_COMPILE}gcc ] ; then  \
 		( unset AS LD LDD CC CPP AR NM STRIP STRIPTOOL OBJCOPY OBJDUMP RANLIB LD_LIBRARY_PATH MAKELEVEL ; \
 		if [ -r ${TOOLCHAIN_CONFIG} ] ; then \
@@ -85,14 +87,14 @@ distclean: clean
 		${ECHO} "Toolchain Build failed!" ; \
 		exit 1 ;\
 	fi
-	@touch .toolchain
+	@touch .toolchain-$(MCU_CORE)
 
 toolclean:
 	$(Q)if [ -d ${CROSS_DIR} ] ; then \
 		chmod -R +w ${CROSS_DIR} ; \
 		${RM} -fr ${CROSS_DIR} ; \
 	fi
-	@${RM} -f .toolchain
+	@${RM} -f .toolchain-$(MCU_CORE)
 
 tags:
 	find . 	-path '*crosstool*' -prune \
@@ -100,7 +102,7 @@ tags:
 		| etags -
 
 
-dep: .toolchain
+dep: .toolchain-$(MCU_CORE)
 	$(Q)rm -f $(DEPFILE)
 	$(Q)make $(DEPFILE)