testsuite: Fix up gcc.dg/pr113693.c for ia32

As I wrote earlier and we've discussed on IRC, with the ia32 _BitInt
enablement patch this testcase FAILs on ia32, there is nothing vectorized in
there, even with -mavx512{vl,bw,dq}, so no dbgcnt messages are emitted.

The following patch instead prunes it.

2024-02-12  Jakub Jelinek  <jakub@redhat.com>

	* gcc.dg/pr113693.c: Guard _BitInt(837) use with
	__BITINT_MAXWIDTH__ >= 837.  Use dg-prune-output instead of
	dg-message for dbgcnt message.