test/tcg/arm: Use -mfloat-abi=soft for test-armv6m-undef

GCC11 from crossbuild-essential-armhf from ubuntu 22.04 errors:
cc1: error: ‘-mfloat-abi=hard’: selected architecture lacks an FPU

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220604032713.174976-1-richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20220613171258.1905715-2-alex.bennee@linaro.org>

tests/tcg/arm/Makefile.softmmu-target

@@ -20,7 +20,7 @@ LDFLAGS+=-nostdlib -N -static
 
 # Specific Test Rules
 
-test-armv6m-undef: EXTRA_CFLAGS+=-mcpu=cortex-m0
+test-armv6m-undef: EXTRA_CFLAGS+=-mcpu=cortex-m0 -mfloat-abi=soft
 
 run-test-armv6m-undef: QEMU_OPTS+=-semihosting -M microbit -kernel
 run-plugin-test-armv6m-undef-%: QEMU_OPTS+=-semihosting -M microbit -kernel