This ports a number of OpenCL and fast-math flags for floating point
over to the new marshalling infrastructure.
As part of this, `Opt{In,Out}FFlag` were enhanced to allow other flags to
imply them, via `DefaultAnyOf<>`. For example:
```
defm signed_zeros : OptOutFFlag<"signed-zeros", ...,
"LangOpts->NoSignedZero",
DefaultAnyOf<[cl_no_signed_zeros, menable_unsafe_fp_math]>>;
```
defines `-fsigned-zeros` (`false`) and `-fno-signed-zeros` (`true`)
linked to the keypath `LangOpts->NoSignedZero`, defaulting to `false`,
but set to `true` implicitly if one of `-cl-no-signed-zeros` or
`-menable-unsafe-fp-math` is on.
Note that the initial patch was written Daniel Grumberg.
Differential Revision: https://reviews.llvm.org/D82756
Jan Svoboda