Drop extra flags from bin/regression script.
Conditionally implement 'Word_mulCheck' in LLVM codegen.

On x86, '@llvm.smul.with.overflow.i64' becomes a call to __mulodi4 amd
'@llvm.umul.with.overflow.i64' becomes a call to __udivdi3.  These are
provided by the LLVM compiler-rt project (and sometimes by libgcc).
In any case, do not depend on non-standard libraries.
Implement 'Real_muladd' in LLVM codegen.

The 'outputPrim' function already handles 'Real_muladd'.