[PATCH, GCC/ARM, 1/10] Fix -mcmse check in libgcc

This patch is part of a patch series to add support for Armv8.1-M
Mainline Security Extensions architecture.

Code to detect whether cmse.c can be buit with -mcmse checks the output
of host GCC when invoked with -mcmse. However, an error from the
compiler does not prevent some minimal output so this always holds true.

2020-01-16  Mihail-Calin Ionescu  <mihail.ionescu@arm.com>
2020-01-16  Thomas Preud'homme  <thomas.preudhomme@arm.com>

	* config/arm/t-arm: Check return value of gcc rather than lack of
	output.

libgcc/ChangeLog

+2020-01-16  Mihail-Calin Ionescu  <mihail.ionescu@arm.com>
+2020-01-16  Thomas Preud'homme  <thomas.preudhomme@arm.com>
+
+	* config/arm/t-arm: Check return value of gcc rather than lack of
+	output.
+
 2020-01-14  Georg-Johann Lay  <avr@gjlay.de>
 
 	* config/avr/lib1funcs.S (skip): Simplify.

libgcc/config/arm/t-arm

@@ -3,7 +3,7 @@ LIB1ASMFUNCS = _thumb1_case_sqi _thumb1_case_uqi _thumb1_case_shi \
 	_thumb1_case_uhi _thumb1_case_si _speculation_barrier
 
 HAVE_CMSE:=$(findstring __ARM_FEATURE_CMSE,$(shell $(gcc_compile_bare) -dM -E - </dev/null))
-ifneq ($(shell $(gcc_compile_bare) -E -mcmse - </dev/null 2>/dev/null),)
+ifeq ($(shell $(gcc_compile_bare) -E -mcmse - </dev/null >/dev/null 2>/dev/null; echo $?),0)
 CMSE_OPTS:=-mcmse
 endif