testsuite: Fix for targets not passing argc/argv [PR116154]

PRU and other simulator targets do not pass any argv arguments
to main.  Instead of erroneously relying on argc==0, use a volatile
variable instead.

I reverted the fix for PR67947 in r6-3891-g8a18fcf4aa1d5c, and made sure
that the updated test case still fails for x86_64:

  $ make check-gcc-c RUNTESTFLAGS="dg-torture.exp=pr67947.c"
  ...
  FAIL: gcc.dg/torture/pr67947.c   -O1  execution test
  ...
  # of expected passes            8
  # of unexpected failures        8

Fix was suggested by Andrew Pinski in PR116154.  Committed as obvious.

	PR testsuite/116154

gcc/testsuite/ChangeLog:

	* gcc.dg/torture/pr67947.c: Use volatile variable instead of
	argc.

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