package/libssh: fix build with Thumb

/home/buildroot/autobuild/instance-3/output-1/build/libssh-0.10.5/src/bignum.c:
 In function 'ssh_make_bignum_string':
/home/buildroot/autobuild/instance-3/output-1/build/libssh-0.10.5/src/bignum.c:64:1:
 sorry, unimplemented: '-fstack-check=specific' for Thumb-1

Fixes:
http://autobuild.buildroot.net/results/82c/82c8e3bb755bc8732a81f05a72f04a96ecc08b4e/

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 0368cd816307ee961bbd17ce2d3827b955b0c204)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libssh/libssh.mk

@@ -17,6 +17,10 @@ LIBSSH_CONF_OPTS = \
 	-DWITH_STACK_PROTECTOR=OFF \
 	-DWITH_EXAMPLES=OFF
 
+ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB),y)
+LIBSSH_CONF_OPTS += -DWITH_STACK_CLASH_PROTECTION=OFF
+endif
+
 ifeq ($(BR2_PACKAGE_LIBSSH_SERVER),y)
 LIBSSH_CONF_OPTS += -DWITH_SERVER=ON
 else