testsuite: Mark non-optimized variants as expensive

When not optimized for speed, the test for PR112344 takes several
seconds to execute on native x86_64, and 15 minutes on PRU target
simulator.  Thus mark those variants as expensive.  The -O2 variant
which originally triggered the PR is not expensive, hence it is
still run by default.

	PR middle-end/112344

gcc/testsuite/ChangeLog:

	* gcc.dg/torture/pr112344.c: Run non-optimized variants only
	if expensive tests are allowed.

Signed-off-by: Dimitar Dimitrov <dimitar@dinux.eu>