Add hadd builtin

(x + y) >> 1 gets changed to:
(x>>1) + (y>>1) + (x&y&1)

Saves us having to do any llvm assembly and overflow checking in the addition.

Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
Add rhadd builtin

rhadd = (x+y+1)>>1

Implemented as:
(x>>1) + (y>>1) + ((x&1)|(y&1))

This prevents us having to do assembly addition and overflow detection

Reviewed-by: Tom Stellard <thomas.stellard@amd.com>