objcopy binary symbol test

A small tidy that allows other symbols or warnings to appear in nm
output, and works around the case problem of windows drive letters
by simply omitting the $srcdir match.

	* testsuite/binutils-all/objcopy.exp (binary_symbol): Check
	objcopy and nm return status.  Don't repeat prune_warnings
	already done in binutils_run.  Match each symbol separately,
	reporting which match failed on a failure.  Don't match
	$srcdir in implicit test.