[Darwin, testsuite ] Fix for PR58321.

[Darwin, testsuite ] Fix for PR58321.

Darwin doesn't emit a .file directive by default
and one of the scan-asm hits for ELF targets comes from
this directive. Adjust for Darwin and explain.

2019-09-06  Iain Sandoe  <iain@sandoe.co.uk>

	Backport from mainline.
	2019-05-20  Iain Sandoe  <iain@sandoe.co.uk>

	PR testsuite/58321
	* gcc.target/i386/memcpy-strategy-3.c: Adjust count for Darwin and
	add a comment as to the reason for the difference.
	* gcc.target/i386/memset-strategy-1.c: Likewise.

From-SVN: r275466