[HLSL] [clang] Add vector version of abs for HLSL

Add vector version of abs as
```
__attribute__((clang_builtin_alias(__builtin_elementwise_abs)))
int2 abs (int2 );
__attribute__((clang_builtin_alias(__builtin_elementwise_abs)))
int3 abs (int3 );
```
To make this work.
Allowed custom type checking builtins to be recelareable.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D133737