Tests: Add automated tests to verify dead code strip

Add an automated tests that validates SwiftBuild build system sets the
dead code stip setting accordingly.

Fixes: #9326
Issue: rdar://163962003

Author: bkhouri

Tests/SwiftBuildSupportTests/SwiftBuildSystemTests.swift

@@ -46,7 +46,7 @@ func withInstantiatedSwiftBuildSystem(
             let observabilitySystem: TestingObservability = ObservabilitySystem.makeForTesting()
             let toolchain = try UserToolchain.default
             let workspace = try Workspace(
-                fileSystem: Basics.localFileSystem,
+                fileSystem: fileSystem,
                 forRootPackage: fixturePath,
                 customManifestLoader: ManifestLoader(toolchain: toolchain),
             )
@@ -178,24 +178,18 @@ struct SwiftBuildSystemTests {
             ),
         ) { swiftBuild, session, observabilityScope, buildParameters in
 
-            #expect(false, "purposely failing")
             let buildSettings = try await swiftBuild.makeBuildParameters(
                 session: session,
                 symbolGraphOptions: nil,
+                setToolchainSetting: false, // Set this to false as SwiftBuild checks the toolchain path
             )
 
-            let expectedValue: String? = switch linkerDeadStripUT {
-                case true:
-                    "YES"
-                case false:
-                    nil
-            }
-
             let synthesizedArgs = try #require(buildSettings.overrides.synthesized)
-            let actual = try #require(synthesizedArgs.table["DEAD_CODE_STRIPPING"], "Code stripping value should not be nil")
-            print("dead strip: \(linkerDeadStripUT) >>> Actual: '\(actual)' expected: '\(expectedValue)'")
-            #expect(actual == expectedValue)
-            #expect(false, "purposely failing")
+            let actual = synthesizedArgs.table["DEAD_CODE_STRIPPING"]
+            #expect(
+                actual == expectedValue,
+                "dead strip: \(linkerDeadStripUT) >>> Actual: '\(actual)' expected: '\(String(describing: expectedValue))'",
+            )
        }
     }
 }