Test: Guard a ManifestSourceGenerationTest and annotateskip message

Guard a test in ManifestSourceGenerationTest based on the compiler
version, and annotate skipped tests with a GitHub issue.

Relates to: #8433
Issue: rdar://148248105

Author: bkhouri

Sources/_InternalTestSupport/XCTAssertHelpers.swift

@@ -76,6 +76,13 @@ public func XCTSkipOnWindows(because reason: String? = nil, skipPlatformCi: Bool
     #endif
 }
 
+public func XCTSkipIfCompilerLessThan6_2() throws {
+    #if compiler(>=6.2)
+    #else
+        throw XCTSkip("Skipping as compiler version is less thann 6.2")
+    #endif
+}
+
 /// An `async`-friendly replacement for `XCTAssertThrowsError`.
 public func XCTAssertAsyncThrowsError<T>(
     _ expression: @autoclosure () async throws -> T,

Tests/WorkspaceTests/ManifestSourceGenerationTests.swift

@@ -796,7 +796,7 @@ final class ManifestSourceGenerationTests: XCTestCase {
     }
 
     func testStrictMemorySafety() async throws {
-        try XCTSkipOnWindows(because: "compilation error:  type 'SwiftSetting' has no member 'strictMemorySafety'")
+        try XCTSkipIfCompilerLessThan6_2()
 
         let manifestContents = """
             // swift-tools-version:6.2
@@ -865,7 +865,7 @@ final class ManifestSourceGenerationTests: XCTestCase {
     }
 
     func testDefaultIsolation() async throws {
-        try XCTSkipOnWindows(because: "there are compilation errors")
+        try XCTSkipOnWindows(because: "https://github.com/swiftlang/swift-package-manager/issues/8543: there are compilation errors")
 
         let manifest = Manifest.createRootManifest(
             displayName: "pkg",