r219557 - [complex] Teach Clang to preserve different-type operands to arithmetic

[Tim Northover]

> Fair enough. I noticed that your patch emits calls to the half-float
> functions, __mulhc3 and __divhc3. The compiler-rt library does not have
> implementations of those for any platform.

I'd hope they're not actually used for C or C++ since __fp16 is still
very much a storage type there. OpenCL compilers may have to deal with
it.

Cheers.

Tim.