cmake: add -fstack-protector-strong on win32

cmake: add -fstack-protector-strong on win32

mingw on RHEL 9 needs -fstack-protector (which adds -lssp), or it fails
with these errors:

  undefined reference to `__stack_chk_fail'
  undefined reference to `__stack_chk_guard'
  undefined reference to `__strcpy_chk'

Commit 8d35b2eceabafbe13458101f8701e3fc49f15d63 mentions that the build
fails with -fstack-protector-strong. Perhaps that only applied to
earlier Ubuntu versions, because Ubuntu Focal can build with
-fstack-protector-strong now.

Signed-off-by: Ken Dreyer <kdreyer@redhat.com>