Tests: adjust LLBuildManifestTests expectations for Windows

This adjusts the expectations to allow Windows to be supported as well
with the use of the paths more thoroughly.  This identified an issue in
the path handling in the manifest generation (tracked as swiftlang#5475).

Tests/BuildTests/LLBuildManifestTests.swift

@@ -20,13 +20,15 @@ final class LLBuildManifestTests: XCTestCase {
     func testBasics() throws {
         var manifest = BuildManifest()
 
+        let root: AbsolutePath = AbsolutePath("/some")
+
         manifest.defaultTarget = "main"
         manifest.addPhonyCmd(
             name: "C.Foo",
             inputs: [
-                .file(AbsolutePath("/some/file.c")),
-                .directory(AbsolutePath("/some/dir")),
-                .directoryStructure(AbsolutePath("/some/dir/structure")),
+                .file(root.appending(components: "file.c")),
+                .directory(root.appending(components: "dir")),
+                .directoryStructure(root.appending(components: "dir", "structure")),
             ],
             outputs: [.virtual("Foo")]
         )
@@ -38,20 +40,22 @@ final class LLBuildManifestTests: XCTestCase {
 
         let contents: String = try fs.readFileContents(AbsolutePath("/manifest.yaml"))
 
-        XCTAssertEqual(contents, """
+        // FIXME(#5475) - use the platform's preferred separator for directory
+        // indicators
+        XCTAssertEqual(contents.replacingOccurrences(of: "\\\\", with: "\\"), """
             client:
               name: basic
             tools: {}
             targets:
               "main": ["<Foo>"]
             default: "main"
             nodes:
-              "/some/dir/structure/":
+              "\(root.appending(components: "dir", "structure"))/":
                 is-directory-structure: true
             commands:
               "C.Foo":
                 tool: phony
-                inputs: ["/some/file.c","/some/dir/","/some/dir/structure/"]
+                inputs: ["\(root.appending(components: "file.c"))","\(root.appending(components: "dir"))/","\(root.appending(components: "dir", "structure"))/"]
                 outputs: ["<Foo>"]
 
 
@@ -61,15 +65,17 @@ final class LLBuildManifestTests: XCTestCase {
     func testShellCommands() throws {
         var manifest = BuildManifest()
 
+        let root: AbsolutePath = AbsolutePath.root
+
         manifest.defaultTarget = "main"
         manifest.addShellCmd(
             name: "shelley",
             description: "Shelley, Keats, and Byron",
             inputs: [
-                .file(AbsolutePath("/file.in]"))
+                .file(root.appending(components: "file.in"))
             ],
             outputs: [
-                .file(AbsolutePath("/file.out"))
+                .file(root.appending(components: "file.out"))
             ],
             arguments: [
                 "foo", "bar", "baz"
@@ -89,18 +95,18 @@ final class LLBuildManifestTests: XCTestCase {
 
         let contents: String = try fs.readFileContents(AbsolutePath("/manifest.yaml"))
 
-        XCTAssertEqual(contents, """
+        XCTAssertEqual(contents.replacingOccurrences(of: "\\\\", with: "\\"), """
             client:
               name: basic
             tools: {}
             targets:
-              "main": ["/file.out"]
+              "main": ["\(root.appending(components: "file.out"))"]
             default: "main"
             commands:
               "shelley":
                 tool: shell
-                inputs: ["/file.in]"]
-                outputs: ["/file.out"]
+                inputs: ["\(root.appending(components: "file.in"))"]
+                outputs: ["\(root.appending(components: "file.out"))"]
                 description: "Shelley, Keats, and Byron"
                 args: ["foo","bar","baz"]
                 env: