[TEST-ONLY] Try renable compilation caching tests

Try again to re-enable caching tests which was marked flaky due to
unstable tests on Xcode Cloud. Re-enable compilation caching tests
except on Xcode Cloud.

Author: cachemeifyoucan

Sources/SWBTestSupport/SkippedTestSupport.swift

@@ -175,6 +175,10 @@ extension Trait where Self == Testing.ConditionTrait {
         return .skipIfEnvironmentVariableSet(key: "GITHUB_ACTIONS")
     }
 
+    package static func skipInXcodeCloud(_ comment: Comment? = nil) -> Self {
+        return .skipIfEnvironmentVariableSet(key: "CI_XCODE_CLOUD")
+    }
+
     package static func requireClangFeatures(_ requiredFeatures: DiscoveredClangToolSpecInfo.FeatureFlag...) -> Self {
         enabled("Clang compiler does not support features: \(requiredFeatures)") {
             let features = try await ConditionTraitContext.shared.clangFeatures

Tests/SWBBuildSystemTests/ClangCompilationCachingTests.swift

@@ -19,8 +19,7 @@ import SWBTestSupport
 import SWBUtil
 
 @Suite(.skipHostOS(.windows, "Windows platform has no CAS support yet"),
-       .requireDependencyScannerPlusCaching,
-       .flaky("A handful of Swift Build CAS tests fail when running the entire test suite"), .bug("rdar://146781403"))
+       .requireDependencyScannerPlusCaching, .skipInXcodeCloud("flaky tests"))
 fileprivate struct ClangCompilationCachingTests: CoreBasedTests {
     let canUseCASPlugin: Bool
     let canUseCASPruning: Bool

Tests/SWBBuildSystemTests/ClangModuleVerifierTests.swift

@@ -192,7 +192,7 @@ fileprivate struct ClangModuleVerifierTests: CoreBasedTests {
     }
 
     @Test(.requireSDKs(.macOS), .requireClangFeatures(.wSystemHeadersInModule), .requireDependencyScannerPlusCaching,
-          .flaky("A handful of Swift Build CAS tests fail when running the entire test suite"), .bug("rdar://146781403"))
+          .skipInXcodeCloud("flaky tests"))
     func cachedBuild() async throws {
         try await withTemporaryDirectory { (tmpDirPath: Path) in
             let archs = ["arm64", "x86_64"]

Tests/SWBBuildSystemTests/SwiftCompilationCachingTests.swift

@@ -20,7 +20,7 @@ import SWBTaskExecution
 import SWBProtocol
 
 @Suite(.requireSwiftFeatures(.compilationCaching),
-       .flaky("A handful of Swift Build CAS tests fail when running the entire test suite"), .bug("rdar://146781403"))
+       .skipInXcodeCloud("flaky tests"))
 fileprivate struct SwiftCompilationCachingTests: CoreBasedTests {
     @Test(.requireSDKs(.iOS))
     func swiftCachingSimple() async throws {