binutils/testsuite: Verify the handling of invalid `r_sym' in relocation

binutils/testsuite: Verify the handling of invalid `r_sym' in relocation

Verify that `strip' terminates gracefully and a correct error message is
produced for a relocation encountered with an invalid symbol index.  No
single relocation number is valid across all targets we support, so pick
a few numbers to choose from depending on the target.

	binutils/
	* testsuite/binutils-all/strip-14.d: New test.
	* testsuite/binutils-all/strip-14rel.s: New test source.
	* testsuite/binutils-all/strip-14rela.s: New test source.
	* testsuite/binutils-all/strip-14mips64.s: New test source.
	* testsuite/binutils-all/objcopy.exp: Run the new test.