Fix testsuite to use newly-built linker for ehdr_start_test_4, and fix
check script to look for the right binding.

gold/
	* testsuite/Makefile.am (ehdr_start_test_4): Fix typo in -B option.
	* testsuite/Makefile.in: Regenerate.
	* testsuite/ehdr_start_test_4.sh: Look for "U" instead of "w".