druntime.expect-trap.dd

Adds `expect`, `[un]likely`, `trap` to `core.builtins`

Adds the functions `expect` and `likely`/unlikely` for branch and value hints for the LDC/GDC compilers.
DMD ignores these hints.

Adds `trap` to lowered to the target dependent trap instruction.
If the target does not have a trap instruction, this intrinsic will be lowered to the call of the abort() function.