Allow "macos" when parsing triples

LLVM target triples support either "macosx" or "macos", so our parsing code should also support both spellings.

Author: neonichu

Sources/TSCUtility/Triple.swift

@@ -108,6 +108,11 @@ public struct Triple: Encodable, Equatable {
             return candidate
         }
 
+        // LLVM target triples support this alternate spelling as well.
+        if string.hasPrefix("macos") {
+            return .macOS
+        }
+
         return nil
     }
 

Tests/TSCUtilityTests/TripleTests.swift

@@ -24,6 +24,10 @@ class TripleTests : XCTestCase {
         let newVersion = "10.12"
         let tripleString = macos!.tripleString(forPlatformVersion: newVersion)
         XCTAssertEqual(tripleString, "x86_64-apple-macosx10.12")
+        let macosNoX = try? Triple("x86_64-apple-macos12.2")
+        XCTAssertNotNil(macosNoX!)
+        XCTAssertEqual(macosNoX!.os, .macOS)
+        XCTAssertEqual(macosNoX!.osVersion, "12.2")
 
         let android = try? Triple("aarch64-unknown-linux-android24")
         XCTAssertNotNil(android)