gold testsuite volatile fixes

Avoid these mainline gcc complaints (C23 WG14 n2743).
copy_test_relro.cc:42:5: error: ‘++’ expression of ‘volatile’-qualified type is deprecated [-Werror=volatile]
icf_test_pr21066.cc:50:55: error: ‘volatile’-qualified parameter is deprecated [-Werror=volatile]

	* testsuite/copy_test_relro.cc (segv): Avoid gcc warning.
	* testsuite/icf_test_pr21066.cc (capture_exception_of_type):
	Likewise.