AArch64: refactor table-driven NEON lookup.

This extracts the table-driven intrinsic lookup phase into a separate
function, to be used by EmitCommonNeonBuiltinExpr soon.

It also simplifies the logic used in that lookup, since VectorCastArgN
and ScalarArgN were actually identical.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201847 91177308-0d34-0410-b5e6-96231b3b80d8
ARM & AArch64: use table for EmitCommonNeonBuiltinExpr

This extends the intrinsic lookup table format slightly, and adds
entries for use the shared ARM/AArch64 definitions. The benefit is
currently smaller than for the SISD intrinsics (there's more custom
code implementing this set), but a few lines are saved and there's
scope for future expansion.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201848 91177308-0d34-0410-b5e6-96231b3b80d8
Remove commas at the end of lists (C++11 again)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201849 91177308-0d34-0410-b5e6-96231b3b80d8