Pass the canonical SDK name to the frontend

The frontend will use this information to control which swiftmodule file
can be loaded according to the SDK in use. Swiftmodule files should only
be used in the context of the SDK used to create them. This will catch
issues with roots and other configuration problems.

rdar://83104265

Author: xymus

Sources/SwiftDriver/Toolchains/DarwinToolchain.swift

@@ -351,6 +351,10 @@ public final class DarwinToolchain: Toolchain {
       commandLine.append(.flag("-target-variant-sdk-version"))
       commandLine.append(.flag(sdkInfo.sdkVersion(for: targetVariantTriple).description))
     }
+
+    commandLine.append(.flag("-target-sdk-name"))
+    commandLine.append(.flag(sdkInfo.canonicalName))
+
     // We should be able to pass down prebuilt module dir for all other SDKs.
     // For macCatalyst, doing so is specifically necessary because -target-sdk-version
     // doesn't always match the macosx sdk version so the compiler may fail to find

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -3091,6 +3091,10 @@ final class SwiftDriverTests: XCTestCase {
           .flag("-target-sdk-version"),
           .flag("10.15.0")
         ]))
+        XCTAssertTrue(frontendJobs[0].commandLine.contains(subsequence: [
+          .flag("-target-sdk-name"),
+          .flag("macosx10.15"),
+        ]))
         XCTAssertEqual(frontendJobs[1].kind, .link)
         XCTAssertTrue(frontendJobs[1].commandLine.contains(subsequence: [
           .flag("-platform_version"),
@@ -3113,6 +3117,8 @@ final class SwiftDriverTests: XCTestCase {
           .flag("10.15.0"),
           .flag("-target-variant-sdk-version"),
           .flag("13.1.0"),
+          .flag("-target-sdk-name"),
+          .flag("macosx10.15"),
         ]))
         XCTAssertEqual(frontendJobs[1].kind, .link)
         XCTAssertTrue(frontendJobs[1].commandLine.contains(subsequence: [
@@ -3139,7 +3145,9 @@ final class SwiftDriverTests: XCTestCase {
           .flag("-target-sdk-version"),
           .flag("10.15.4"),
           .flag("-target-variant-sdk-version"),
-          .flag("13.4.0")
+          .flag("13.4.0"),
+          .flag("-target-sdk-name"),
+          .flag("macosx10.15.4"),
         ]))
         XCTAssertEqual(frontendJobs[1].kind, .link)
         XCTAssertTrue(frontendJobs[1].commandLine.contains(subsequence: [
@@ -3166,7 +3174,9 @@ final class SwiftDriverTests: XCTestCase {
           .flag("-target-sdk-version"),
           .flag("13.4.0"),
           .flag("-target-variant-sdk-version"),
-          .flag("10.15.4")
+          .flag("10.15.4"),
+          .flag("-target-sdk-name"),
+          .flag("macosx10.15.4"),
         ]))
         XCTAssertEqual(frontendJobs[1].kind, .link)
         XCTAssertTrue(frontendJobs[1].commandLine.contains(subsequence: [