[stdlib] Added PowerPC 32-bit support

[colemancda]

Added patches to cross compile the Swift stdlib for the PowerPC 32-bit architecture.

[ghost]

Genius， I like your pull request，fantastic

[CodaFi]

Compiler changes LGTM.

Would like stdlib’s eyes on this for the rest.

@swift-ci test

[CodaFi]

You may want to update the Swift driver here https://github.com/apple/swift-driver/blob/0f9f247c8cc3d225dbbc263b1ec082bf2c8675fe/Sources/SwiftDriver/Jobs/GenericUnixToolchain%2BLinkerSupport.swift

we should already accept the ppc triple family.

[finagolfin]

Heh, nice, are you actually building the Swift compiler for 32-bit PowerPC too? If so, not hitting this C++ static assert that I hit with Android armv7 a couple months ago?

[colemancda]

@buttaface No, I compile a patched Swift 5.5.3 compiler for Aarch64 (Debian on M1 Pro) and cross compile the stdlib using cmake and buildroot. I am building a qemu mac99 image right now. This is also the strategy I used to cross compile Swift 5.5.3 for Armv7. Only 1 patch was needed provided by @uraimo to fix weak references.

[colemancda]

I have had to make changes to LLVM that I will be submitting. Mainly in TargetInfo.cpp.

[colemancda]

Right now I am getting this error:

In file included from ../stdlib/public/runtime/Casting.cpp:18:
In file included from ../include/swift/Runtime/Casting.h:20:
In file included from ../include/swift/Runtime/Metadata.h:20:
../include/swift/ABI/Metadata.h:777:50: error: 'swift_context' parameter can only be used with swiftcall or swiftasynccall calling convention
  SWIFT_CC(swift) void(SWIFT_CONTEXT HeapObject *);

[colemancda]

LLVM patches
swiftlang/llvm-project#4022

[CodaFi]

@swift-ci test