tpm2-tss: fix build without stack smashing protection (SSP)

Restore a configuration environment setup that was incorrectly removed
along with the upgrade to version 2.1.0.

Fixes:
  http://autobuild.buildroot.net/results/44221140fb8e2ddcb7d624e657b92a59375c02dd
  http://autobuild.buildroot.net/results/08b2a8a4bdd1c38703626a4fc37dab31dce98f49
  http://autobuild.buildroot.net/results/e469b47a6c8f1e8812325fd2860345105052316c
  http://autobuild.buildroot.net/results/f230fe6bbeb8b22d2b5b7cfb3f0ac4b3b936dc37
  http://autobuild.buildroot.net/results/ceb824033888086f6dde22c66d5b5f692a253c7e
  http://autobuild.buildroot.net/results/f863947a7384cb754706e6c346d222be59ad4136

Signed-off-by: Carlos Santos <casantos@datacom.ind.br>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/tpm2-tss/tpm2-tss.mk

@@ -12,4 +12,8 @@ TPM2_TSS_INSTALL_STAGING = YES
 TPM2_TSS_DEPENDENCIES = liburiparser openssl host-pkgconf
 TPM2_TSS_CONF_OPTS = --with-crypto=ossl --disable-doxygen-doc
 
+# configure.ac doesn't contain a link test, so it doesn't detect when
+# libssp is missing.
+TPM2_TSS_CONF_ENV = ax_cv_check_cflags___________Wall__Werror_______fstack_protector_all=$(if $(BR2_TOOLCHAIN_HAS_SSP),yes,no)
+
 $(eval $(autotools-package))