nvptx: Specify '-mno-alias' for 'gcc.dg/pr60797.c' [PR60797, PR104957]

2014 Subversion r209299 (Git commit 8330537b)
"Fix PR60797" added this test case, which we now amend so that it's able to
test its thing also in '--target=nvptx-none' configurations with symbol alias
support enabled (..., and test nvptx '-mno-alias').

	PR middle-end/60797
	PR target/104957
	gcc/testsuite/
	* gcc.dg/pr60797.c: For nvptx, specify '-mno-alias'.