ld/testsuite: force warnings when dealing with execstack tests

Binutils can be configured to avoid printing the execstack or RWD
segment warnings. In this case, the first test of PR ld/29072 will fail.
Fix that by always manually forcing the warnings for it.

ld/ChangeLog:

	* testsuite/ld-elf/elf.exp (PR ld/29072): Force execstack and
	RWD segment warnings.
1 file changed