gcc: pass explicit gcc_cv_libc_provides_ssp also to gcc-final

gcc: pass explicit gcc_cv_libc_provides_ssp also to gcc-final

During the gcc-initial build, we already pass
gcc_cv_libc_provides_ssp=yes explicitly when SSP support will be
available in the C library: at this point in time the C library is not
yet built, so gcc cannot detect if it will support SSP or not.

However, it turns out that there are some situations for which it is
also useful to tell gcc explicitly whether the SSP support is
available or not: the gcc logic to decide whether uClibc has SSP
support or not is broken since uClibc-ng bumped the glibc version it
pretends to be.

So, this commit makes sure that we explicitly pass
gcc_cv_libc_provides_ssp both to gcc-initial and gcc-final, and that
we're always passing either 'yes' or 'no'.

Fixes:

   http://autobuild.buildroot.org/results/778/778e6309ba834cc70f8243a4f6c664c0bcaeb7c5/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>