Importer support for float80

[stephentyrone]

Teach the importer to map between C's long double type and Float80 on non-Windows x86_64 and i386 platforms, and take advantage of this mapping to clean up a few details in the stdlib.

This also makes available the full set of platform math functions for Float80.

Resolves SR-2046.

[stephentyrone]

@swift-ci Please test.

[stephentyrone]

@moiseev The stdlib changes here are pretty minimal, but can you take a quick look?

[jrose-apple]

Importer side looks good, and none of the rest looks like anything alarming.

[vivkong]

Got build failures on Linux on Z (s390x) related to this commit:

/home/swiftbuild/workspace/Swift/CONFIG/FIVE/GIT_BRANCH/master/label/csz25097/swift/stdlib/public/Platform/tgmath.swift.gyb:207:34: error: 'Float80' is unavailable: Float80 is only available on non-Windows x86 targets.
09:08:10 public func cos(_ x: Float80) -> Float80 {
09:08:10                                  ^~~~~~~
09:08:10 Swift.Float80:2:15: note: 'Float80' has been explicitly marked unavailable here
09:08:10 public struct Float80 {
09:08:10               ^
09:08:10 /home/swiftbuild/workspace/Swift/CONFIG/FIVE/GIT_BRANCH/master/label/csz25097/swift/stdlib/public/Platform/tgmath.swift.gyb:207:22: error: 'Float80' is unavailable: Float80 is only available on non-Windows x86 targets.
09:08:10 public func cos(_ x: Float80) -> Float80 {
09:08:10                      ^~~~~~~
09:08:10 Swift.Float80:2:15: note: 'Float80' has been explicitly marked unavailable here
09:08:10 public struct Float80 {
09:08:10               ^

(and others)

Any ideas on how to fix this? Thanks

[jrose-apple]

Looks like Steve forgot one of the #if blocks, the one for OverlayFloatTypes. Feel free to put up a PR for that if you don't want to wait for him.

[vivkong]

ah OK. I have a patch ready. Will create a PR. Thanks @jrose-apple!

[stephentyrone]

Great, thanks @vivkong! I'm happy to review.

[ricksentam]

@stephentyrone

• #37189