build: allow building crossgcc when .config exists

Under some circumstances the coreboot toolchain test prevented
building crossgcc, which is counter-productive: If a .config file
exists but no suitable .xcompile.

Don't assume anything about the tree when building crossgcc or
crosstools targets.

Change-Id: I4d6e7a88908dc967342daf30df0fcbcc269ae63d
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/5584
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-by: Martin Roth <martin.roth@se-eng.com>

Makefile

@@ -97,7 +97,7 @@ ifeq ($(strip $(HAVE_DOTCONFIG)),)
 NOCOMPILE:=1
 endif
 ifneq ($(MAKECMDGOALS),)
-ifneq ($(filter %config %clean,$(MAKECMDGOALS)),)
+ifneq ($(filter %config %clean cross%,$(MAKECMDGOALS)),)
 NOCOMPILE:=1
 endif
 ifeq ($(MAKECMDGOALS), %clean)