R600: Fix formatting of intrinsic definitions.

It makes more sense for the GCCBuiltin name to come immediately
after the ID name.
R600/SI: Fix div_scale intrinsic.

The operand that must match one of the others does matter,
and implement selecting for it.
R600/SI: Verify restrictions on div_scale operands.
Recommit 211309 (StringMap::insert), reverted in 211328 due to issues with private, but non-deleted, move members.

Certain versions of GCC (~4.7) couldn't handle the SFINAE on access
control, but with "= delete" (hidden behind a macro for portability)
this issue is worked around/addressed.

Patch by Agustín Bergé