Build system: Avoid executable stack.

Found in res_geolocation, but I believe others may have similar issues,
thus not linking to a specific issue.

Essentially gcc doesn't mark the stack for being non-executable unless
it's compiling the source, this informs ld via gcc to mark the object as
not requiring an executable stack (which a binary blob obviously
doesn't).

ASTERISK-30321

Change-Id: I71bcc2fd1fe0c82a28b3257405d6f2b566fd9bfc
Signed-off-by: Jaco Kroon <jaco@uls.co.za>