m4: Do not use SIGSTKSZ

Fixes
../../m4-1.4.18/lib/c-stack.c:55:26: error: missing binary operator before token "("
   55 | #elif HAVE_LIBSIGSEGV && SIGSTKSZ < 16384
      |                          ^~~~~~~~

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>