More alloca cleanups.

More alloca cleanups.

* bootstrap (gnulib_modules): Remove alloca.  Bison doesn't need
it itself.
* src/main.c (main) [C_ALLOCA]: Don't flush alloca'ed memory; we
don't use alloca any more.

* data/yacc.c [YYSTACK_USE_ALLOCA && !defined __GNUC__ && ! defined
__BUILTIN_VA_ARG_INCR && ! defined _AIX && ! defined _MSC_VER &&
(defined alloca || defined _ALLOCA_H)]: Don't include <stdlib.h>;
not needed in this case.
* tests/torture.at (Exploding the Stack Size with Alloca): Adjust
to match yacc.c, to test more hosts.