SwiftDriver: use swiftrtT.obj for static linking on Windows

Use the PIE registrar on Windows when building with the static standard
library. This is important as we will have a loaclly defined
implementation of `swift_addNewDSOImage` and thus cannot use the PIC
version which expects that to be dynamically linked (imported).

Author: compnerd

Sources/SwiftDriver/Jobs/WindowsToolchain+LinkerSupport.swift

@@ -192,7 +192,12 @@ extension WindowsToolchain {
                           .appending(components: targetTriple.platformName() ?? "",
                                      architecture(for: targetTriple))
       }
-      commandLine.appendPath(rsrc.appending(component: "swiftrt.obj"))
+
+      if parsedOptions.hasArgument(.staticStdlib) {
+          commandLine.appendPath(rsrc.appending(component: "swiftrtT.obj"))
+      } else {
+          commandLine.appendPath(rsrc.appending(component: "swiftrt.obj"))
+      }
     }
 
     commandLine.append(contentsOf: inputs.compactMap { (input: TypedVirtualPath) -> Job.ArgTemplate? in

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -8706,6 +8706,21 @@ final class SwiftDriverTests: XCTestCase {
       XCTAssertJobInvocationMatches(job, .path(.absolute(SDKROOT.appending(components: "usr", "lib", "swift", platform, arch, "swiftrt.obj"))))
     }
 
+    do {
+      var env = ProcessEnv.block
+      env["SDKROOT"] = SDKROOT.nativePathString(escaped: false)
+
+      var driver = try Driver(args: [
+        "swiftc", "-emit-library", "-o", "library.dll", "library.obj", "-static-stdlib",
+      ], env: env)
+      let jobs = try driver.planBuild().removingAutolinkExtractJobs()
+      XCTAssertEqual(jobs.count, 1)
+      let job = jobs.first!
+      XCTAssertEqual(job.kind, .link)
+      XCTAssertJobInvocationMatches(job, .path(.absolute(SDKROOT.appending(components: "usr", "lib", "swift", platform, arch, "swiftrtT.obj"))))
+      XCTAssertFalse(job.commandLine.contains(.path(.absolute(SDKROOT.appending(components: "usr", "lib", "swift", platform, arch, "swiftrt.obj")))))
+    }
+
     do {
       var env = ProcessEnv.block
       env["SDKROOT"] = SDKROOT.nativePathString(escaped: false)