[tilegx] Intrinsic support for mfspr/mtspr.

  it's useful for accessing cycle counter.

   __builtin_tilegx_mfspr(SPR_CYCLE)
[tilegx] Auto-vectorize support for add/sub.

  but there is performance regression when auto-vectorizer enabled.

  for example, for the following simple loop

    void test4(int* restrict a, int* restrict b, int k)
      {
        for (int i = 0; i < k; i++)
          {
            a[i] = a[i] + b[i];
          }
      }

  a rough profiling result:

            no auto-vec     autovec
  gcc-4.4.6  800 cycles      650
  clang      1400            2000
[tilegx] Improve asm output format (no function change)

  use "op\tdest" instead of "op dest", the output looks better.
More conveinent for people to do assembly analysis.