[Bug target/51955] _mm_setzero_si128 intrinsic causes segfault without -O

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51955

--- Comment #5 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-01-23 
10:50:52 UTC ---
void _start() {
    main();
}

isn't properly aligning the stack for the ABI GCC assumes.  Simply drop it.