* Add availability information to the new Math function protocols
The protocols ElementaryFunctions, RealFunctions, and Real are new in Swift 5.1 and accordingly need to have availability attached to them for platforms that are ABI-stable. The actual implementation hooks (static functions) are unconditionally defined on scalar types and marked @_alwaysEmitIntoClient, so they are available even when targeting older library versions, but the protocols themselves, and anything defined in terms of them (the global functions and the SIMD extensions) is only available when targeting library versions that have the new protocols.
* Additionally provide concrete implementations of signGamma for each stdlib-builtin floating-point type.
* Remove Real[Functions] protocols pending re-review
Temporarily pull these back so we can make minor tweaks to the design and get a re-review on SE.
This implements the protocols and static functions proposed in SE-0246, plus some initial test coverage. It also has some rough accompanying cleanup of tgmath. It does not include the globals (on scalars or SIMD types) nor does it deprecate much in tgmath.h.
* Revert "Merge pull request #23791 from compnerd/you-know-nothing-clang"
This reverts commit 5150981150, reversing
changes made to 8fc305c03e.
* Revert "Merge pull request #23780 from compnerd/math-is-terrible"
This reverts commit 2d7fedd25f, reversing
changes made to 0205150b8f.
* Revert "Merge pull request #23140 from stephentyrone/mafs"
This reverts commit 777750dc51, reversing
changes made to 0c8920e747.
