Makefile: Disable stack-usage check for ARC

With the most recent tools for ARC (arc-2017.09) in case of
"naked" function compiler throws a warning:
---------------------------------->8-----------------------------
board/synopsys/hsdk/hsdk.c: In function 'hsdk_core_init_f':
board/synopsys/hsdk/hsdk.c:345:1: warning: stack usage computation not supported for this target
 }
 ^
---------------------------------->8-----------------------------

That happens because the compiler doesn't handle "naked" functions
as a special case where stack calculation shouldn't be done.

But for now until this is fixed in GCC to get clean buildman output
we're disabling stack-usage check for ARC.

See https://lists.denx.de/pipermail/u-boot/2018-April/324455.html
for more background.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Tom Rini <trini@konsulko.com>

Makefile

@@ -600,9 +600,13 @@ KBUILD_CFLAGS	+= -g
 KBUILD_AFLAGS	+= -g
 
 # Report stack usage if supported
+# ARC tools based on GCC 7.1 has an issue with stack usage
+# with naked functions, see commit message for more details
+ifndef CONFIG_ARC
 ifeq ($(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-stack-usage.sh $(CC)),y)
 	KBUILD_CFLAGS += -fstack-usage
 endif
+endif
 
 KBUILD_CFLAGS += $(call cc-option,-Wno-format-nonliteral)