dev-util/mingw64-runtime: avoid libssp references without -fstack-protector

dev-util/mingw64-runtime: avoid libssp references without -fstack-protector

mingw64-runtime-7.0.0 added basic support of _FORTIFY_SOURCE to harden
strcpy() and memcpy() via __strcpy_chk() __memcpy_chk() similar to glibc.

Unfortunately that imposes a new dependency on every caller that defines
_FORTIFY_SOURCE to link against libssp as minw64-runtime does not provide
__strcpy_chk() and friends. For comparison glibc does provide __strcpy_chk.

To avoid widespread breakage (including build failure of USE=ssp gcc itself)
we enable __strcpy_chk() checks only when -fstack-protector* options are set.

Package-Manager: Portage-2.3.85, Repoman-2.3.20
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>