Tests: make BuildPlanTests less reliant on the environment on Windows

The Windows toolchain does not find the default linker by default as
that requires the sourcing of Visual Studio's scripts to setup the
environment.  Adjust the tests to explicitly specify the linker to
ensure that the toolchain is usable on Windows without constraint on the
environment.  While in the area, adjust the expectations to account for
platform path spellings.  This allows us to pass these tests on Windows
now.

Author: compnerd

Tests/BuildTests/BuildPlanTests.swift

@@ -3536,7 +3536,7 @@ final class BuildPlanTests: XCTestCase {
             toolset: .init(
                 knownTools: [
                     .cCompiler: .init(extraCLIOptions: ["-I/fake/sdk/sysroot", "-clang-flag-from-json"]),
-                    .swiftCompiler: .init(extraCLIOptions: ["-swift-flag-from-json"])
+                    .swiftCompiler: .init(extraCLIOptions: ["-swift-flag-from-json", "-use-ld=lld"]),
                 ],
                 rootPaths: try UserToolchain.default.destination.toolset.rootPaths
             ),
@@ -3567,7 +3567,18 @@ final class BuildPlanTests: XCTestCase {
         XCTAssertMatch(try lib.basicArguments(isCXX: false), args)
 
         let exe = try result.target(for: "exe").swiftTarget().compileArguments()
-        XCTAssertMatch(exe, ["-module-cache-path", "\(buildPath.appending(components: "ModuleCache"))", .anySequence, "-swift-flag-from-json", "-g", "-swift-command-line-flag", .anySequence, "-Xcc", "-clang-flag-from-json", "-Xcc", "-g", "-Xcc", "-clang-command-line-flag"])
+        XCTAssertMatch(exe, [
+            "-module-cache-path",
+            "\(buildPath.appending(components: "ModuleCache"))",
+            .anySequence,
+            "-swift-flag-from-json",
+            .anySequence,
+            "-swift-command-line-flag",
+            .anySequence,
+            "-Xcc", "-clang-flag-from-json",
+            .anySequence,
+            "-Xcc", "-clang-command-line-flag"
+        ])
     }
 
     func testUserToolchainWithToolsetCompileFlags() throws {
@@ -3757,7 +3768,10 @@ final class BuildPlanTests: XCTestCase {
             properties: .init(
                 sdkRootPath: "/fake/sdk",
                 includeSearchPaths: [sdkIncludeSearchPath],
-                librarySearchPaths: [sdkLibrarySearchPath]))
+                librarySearchPaths: [sdkLibrarySearchPath]),
+            toolset: .init(knownTools: [
+                .swiftCompiler: .init(extraCLIOptions: ["-use-ld=lld"]),
+            ]))
         let toolchain = try UserToolchain(destination: destination)
         let buildParameters = mockBuildParameters(toolchain: toolchain)
         let result = try BuildPlanResult(plan: BuildPlan(
@@ -3770,17 +3784,17 @@ final class BuildPlanTests: XCTestCase {
 
         // Compile C Target
         let cLibCompileArguments = try result.target(for: "cLib").clangTarget().basicArguments(isCXX: false)
-        let cLibCompileArgumentsPattern: [StringPattern] = ["-I", "\(sdkIncludeSearchPath)"]
+        let cLibCompileArgumentsPattern: [StringPattern] = ["-I", "\(AbsolutePath(sdkIncludeSearchPath)._nativePathString(escaped: false))"]
         XCTAssertMatch(cLibCompileArguments, cLibCompileArgumentsPattern)
 
         // Compile Swift Target
         let exeCompileArguments = try result.target(for: "exe").swiftTarget().compileArguments()
-        let exeCompileArgumentsPattern: [StringPattern] = ["-I", "\(sdkIncludeSearchPath)"]
+        let exeCompileArgumentsPattern: [StringPattern] = ["-I", "\(AbsolutePath(sdkIncludeSearchPath)._nativePathString(escaped: false))"]
         XCTAssertMatch(exeCompileArguments, exeCompileArgumentsPattern)
 
         // Link Product
         let exeLinkArguments = try result.buildProduct(for: "exe").linkArguments()
-        let exeLinkArgumentsPattern: [StringPattern] = ["-L", "\(sdkIncludeSearchPath)"]
+        let exeLinkArgumentsPattern: [StringPattern] = ["-L", "\(AbsolutePath(sdkIncludeSearchPath)._nativePathString(escaped: false))"]
         XCTAssertMatch(exeLinkArguments, exeLinkArgumentsPattern)
     }