RISC-V: Mark unsupported gas testcases

RISC-V: Mark unsupported gas testcases

There are individual comments that explain why each test isn't
supported, but the vast majority of them are due to RISC-V's aggressive
linker relaxation.  The SLEB test cases should eventually be supported,
but the remaining ones probably won't ever be.

2017-10-18  Palmer Dabbelt  <palmer@dabbelt.com>

        * testsuite/gas/all/align.d: Mark as unsupported on RISC-V.
        testsuite/gas/all/relax.d: Likewise.
        testsuite/gas/all/sleb128-2.d: Likewise.
        testsuite/gas/all/sleb128-4.d: Likewise.
        testsuite/gas/all/sleb128-5.d: Likewise.
        testsuite/gas/all/sleb128-7.d: Likewise.
        testsuite/gas/elf/section11.d: Likewise.
        testsuite/gas/all/gas.exp (diff1.s): Likewise.