Align the stack to a 16 byte boundary so that we can safely call functions

that use SSE. The compiler does attempt to do this in main() but not very
successfully - it still manages to use unaligned offsets from %ebp in some
cases. Also we need to have an aligned stack in case something uses SSE
via _init().

MFC After: 1 week

lib/csu/i386-elf/crt1.c

@@ -78,6 +78,9 @@ _start(char *ap, ...)
 	char **env;
 	const char *s;
 
+#ifdef __GNUC__
+	__asm__("and $0xfffffff0,%esp");
+#endif
 	cleanup = get_rtld_cleanup();
 	argv = ≈
 	argc = *(long *)(void *)(argv - 1);