Android: fix ABI triple detection, disable C++ modules flags, and bring back bootstrap script tweaks

[finagolfin]

This pull redoes the previous tweaks for the old non-CMake bootstrap script. Since the new bootstrap script rebuilds llbuild by using its Package.swift, rather than the prior approach of linking against the llbuild already built by the Swift build-script, I had problems when building llbuild with SPM because of the C++ modules support.

Removing those flags, as for Windows, gets llbuild and SPM built, with some of those BuildPlanTests now failing, as they explicitly look for that flag.

In the process, I discovered that the isAndroid() function I added earlier wasn't working right, as it would only detect androideabi and not android. As the two appear to be equivalent, with LLVM just turning the former into the latter, I had the SPM Triple parser do the same.

I also had to modify llbuild's Package.swift to link in ncurses on Android:

diff --git a/Package.swift b/Package.swift
index 6141342..6a20665 100644
--- a/Package.swift
+++ b/Package.swift
@@ -150,7 +150,7 @@ let package = Package(
             name: "llvmSupport",
             dependencies: ["llvmDemangle"],
             path: "lib/llvm/Support",
-            linkerSettings: [.linkedLibrary("ncurses", .when(platforms: [.linux, .macOS]))]
+            linkerSettings: [.linkedLibrary("ncurses", .when(platforms: [.linux, .macOS, .android]))]
         ),
     ],
     cxxLanguageStandard: .cxx14

which then required changing the SPM version where that's supported locally, so llbuild's SPM manifest could use it:

diff --git a/Sources/PackageDescription4/SupportedPlatforms.swift b/Sources/PackageDescription4/SupportedPlatforms.swift
index 06439ebe..8bd41f13 100644
--- a/Sources/PackageDescription4/SupportedPlatforms.swift
+++ b/Sources/PackageDescription4/SupportedPlatforms.swift
@@ -39,7 +39,7 @@ public struct Platform: Encodable {
     public static let windows: Platform = Platform(name: "windows")
 
     /// The Android platform
-    @available(_PackageDescription, introduced: 5.2)
+    @available(_PackageDescription, introduced: 5.0)
     public static let android: Platform = Platform(name: "android")
 }
 

Hopefully, that won't be necessary once Swift 5.2 ships though.

[finagolfin]

This raw value was added years back and never used until my recent native Android pulls, so should be fine to change.

[aciidgh]

Hey, wanna try using the new swift -print-target-info to get the triple automatically?

[finagolfin]

I'll try it out.

[aciidgh]

We can probably drive this based on swift -print-target-info as well 🤔

[aciidgh]

cc @DougGregor

[DougGregor]

Yeah, ‘-print-target-info’ indicates whether one should use rpaths

[finagolfin]

@aciidb0mb3r, do you mean extracting the relative path from the provided runtimeLibraryPaths instead of hardcoding it for each platform here? Because librariesRequireRPath is currently useless on non-Darwin platforms, always returning false.

[aciidgh]

Exacting the "linux" or "android" bit from the triple should be good enough, I think? @DougGregor or @brentdax might have better ideas though.

Anyway, I don't want to block your PR on this stuff so I am happy to take this patch and perhaps you can try swift -print-target-info in a follow on patch 😃

[finagolfin]

Sounds good, I'll try it in my next pull.

[aciidgh]

@swift-ci smoke test