Makefile: Add a 'checkthumb' rule

This rule confirms that if we're on ARM and we have enabled THUMB builds
that we have a new enough toolchain to produce a working binary.

Changes in v2:
- Switch to ALL-$(CONFIG_SYS_THUMB_BUILD) in arch/arm/config.mk (Mike F)
- Simplfy checkthumb test after doing the above

Signed-off-by: Tom Rini <trini@ti.com>
Acked-by: Mike Frysinger <vapier@gentoo.org>

Makefile

@@ -556,6 +556,13 @@ SYSTEM_MAP = \
 $(obj)System.map:	$(obj)u-boot
 		@$(call SYSTEM_MAP,$<) > $(obj)System.map
 
+checkthumb:
+	@if test $(call cc-version) -lt 0404; then \
+		echo -n '*** Your GCC does not produce working '; \
+		echo 'binaries in THUMB mode.'; \
+		echo '*** Your board is configured for THUMB mode.'; \
+		false; \
+	fi
 #
 # Auto-generate the autoconf.mk file (which is included by all makefiles)
 #

arch/arm/config.mk

@@ -44,6 +44,11 @@ PF_CPPFLAGS_ARM := $(call cc-option,-marm,) \
 		$(call cc-option,-mno-thumb-interwork,)
 endif
 
+# Only test once
+ifneq ($(CONFIG_SPL_BUILD),y)
+ALL-$(CONFIG_SYS_THUMB_BUILD)	+= checkthumb
+endif
+
 # Try if EABI is supported, else fall back to old API,
 # i. e. for example:
 # - with ELDK 4.2 (EABI supported), use: