RISC-V: avoid ld crashes due to bogus use by testcases

Specifying a little-endian emulation isn't very helpful when the target is
big-endian (and hence gas defaults to that). Surely the linker better
wouldn't crash when invoked like this, but making sure of this isn't the
purpose of any of these tests (afaict). Make assembly output match linker
options.

With this the ld testsuite completes successfully for me. binutils and gas
testsuites still have issues.