ld testsuite output files

ld testsuite output files

In many cases the output of one run_cc_link_tests test is used as
input for another test.  I hit a case where some system change caused
errors when compiling object files, but the old .so output from a
previous test run was still there, and then was used in following
tests.

	* testsuite/lib/ld-lib.exp (run_ld_link_tests): Delete output
	file before building.
	(run_ld_link_exec_tests, run_cc_link_tests): Likewise.