SwiftDriver: add support for baremetal targets (to reflect swiftlang/swift#35970)

Author: kubamracek

Sources/SwiftDriver/Driver/Driver.swift

@@ -2936,7 +2936,7 @@ extension Triple {
       return DarwinToolchain.self
     case .linux:
       return GenericUnixToolchain.self
-    case .freeBSD, .haiku, .openbsd:
+    case .freeBSD, .haiku, .openbsd, .noneOS:
       return GenericUnixToolchain.self
     case .wasi:
       return WebAssemblyToolchain.self

Sources/SwiftDriver/Utilities/Triple+Platforms.swift

@@ -314,6 +314,8 @@ extension Triple {
       return "haiku"
     case .wasi:
       return "wasi"
+    case .noneOS:
+      return nil
 
     // Explicitly spell out the remaining cases to force a compile error when
     // Triple updates

Sources/SwiftDriver/Utilities/Triple.swift

@@ -1109,6 +1109,7 @@ extension Triple {
     case hurd
     case wasi
     case emscripten
+    case noneOS // 'OS' suffix purely to avoid name clash with Optional.none
 
     var name: String {
       return rawValue
@@ -1188,6 +1189,8 @@ extension Triple {
         return .wasi
       case _ where os.hasPrefix("emscripten"):
         return .emscripten
+      case _ where os.hasPrefix("none"):
+        return .noneOS
       default:
         return nil
       }

Tests/SwiftDriverTests/TripleTests.swift

@@ -187,6 +187,12 @@ final class TripleTests: XCTestCase {
     T = Triple("arm-none-none-eabi")
     XCTAssertEqual(T.arch, Triple.Arch.arm)
     XCTAssertEqual(T.vendor, nil)
+    XCTAssertEqual(T.os, .noneOS)
+    XCTAssertEqual(T.environment, Triple.Environment.eabi)
+
+    T = Triple("arm-none-unknown-eabi")
+    XCTAssertEqual(T.arch, Triple.Arch.arm)
+    XCTAssertEqual(T.vendor, nil)
     XCTAssertEqual(T.os, nil)
     XCTAssertEqual(T.environment, Triple.Environment.eabi)
 
@@ -723,7 +729,7 @@ final class TripleTests: XCTestCase {
     assertNormalizesEqual("i686-linux",
               "i686-unknown-linux") // i686-pc-linux-gnu
     assertNormalizesEqual("arm-none-eabi",
-              "arm-none-unknown-eabi") // arm-none-eabi
+              "arm-unknown-none-eabi") // arm-none-eabi
     assertNormalizesEqual("wasm32-wasi",
               "wasm32-unknown-wasi") // wasm32-unknown-wasi
     assertNormalizesEqual("wasm64-wasi",