toolchain/helpers.mk: use int as main() return type in checks

Although -Wmain-return-type is not considered as error (unlike
-Wimplicit-int), but just a warning, let's fix it for the future.

<stdin>:1:1: warning: return type of 'main' is not 'int' [-Wmain-return-type]

Signed-off-by: Petr Vorel <petr.vorel@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

toolchain/helpers.mk

@@ -483,7 +483,7 @@ check_unusable_toolchain = \
 #
 check_toolchain_ssp = \
 	__CROSS_CC=$(strip $1) ; \
-	__HAS_SSP=`echo 'void main(){}' | $${__CROSS_CC} -Werror -fstack-protector -x c - -o $(BUILD_DIR)/.br-toolchain-test.tmp >/dev/null 2>&1 && echo y` ; \
+	__HAS_SSP=`echo 'int main(){}' | $${__CROSS_CC} -Werror -fstack-protector -x c - -o $(BUILD_DIR)/.br-toolchain-test.tmp >/dev/null 2>&1 && echo y` ; \
 	if [ "$(BR2_TOOLCHAIN_HAS_SSP)" != "y" -a "$${__HAS_SSP}" = "y" ] ; then \
 		echo "SSP support available in this toolchain, please enable BR2_TOOLCHAIN_EXTERNAL_HAS_SSP" ; \
 		exit 1 ; \
@@ -494,7 +494,7 @@ check_toolchain_ssp = \
 	fi ; \
 	__SSP_OPTION=$(2); \
 	if [ -n "$${__SSP_OPTION}" ] ; then \
-		if ! echo 'void main(){}' | $${__CROSS_CC} -Werror $${__SSP_OPTION} -x c - -o $(BUILD_DIR)/.br-toolchain-test.tmp >/dev/null 2>&1 ; then \
+		if ! echo 'int main(){}' | $${__CROSS_CC} -Werror $${__SSP_OPTION} -x c - -o $(BUILD_DIR)/.br-toolchain-test.tmp >/dev/null 2>&1 ; then \
 			echo "SSP option $${__SSP_OPTION} not available in this toolchain, please select another SSP level" ; \
 			exit 1 ; \
 		fi; \