[xcodegen] Show caveat for --stdlib-swift too

While here, also add a caveat for the fact that
`--stdlib-swift` is disabled by default since it's
surprised a couple of folks now.

Author: hamishknight

utils/swift-xcodegen/Sources/swift-xcodegen/SwiftXcodegen.swift

@@ -288,18 +288,38 @@ struct SwiftXcodegen: AsyncParsableCommand, Sendable {
     return task
   }
 
-  func generate() async throws {
-    let buildDirPath = buildDir.absoluteInWorkingDir.resolvingSymlinks
-    log.info("Generating project for '\(buildDirPath)'...")
+  func showCaveatsIfNeeded() {
+    guard log.logLevel <= .note else { return }
 
+    var notes: [String] = []
     if projectOpts.useBuildableFolders {
-      log.note("""
-        Buildable folders are enabled by default, which requires Xcode 16. You \
-        can pass '--no-buildable-folders' to disable this. See the '--help' entry \
-        for more info.
+      notes.append("""
+        - Buildable folders are enabled by default, which requires Xcode 16. You
+          can pass '--no-buildable-folders' to disable this. See the '--help'
+          entry for more info.
         """)
     }
 
+    if !projectOpts.addStdlibSwift {
+      notes.append("""
+        - Swift standard library targets are disabled by default since they require
+          using a development snapshot of Swift with Xcode. You can pass '--stdlib-swift'
+          to enable. See the '--help' entry for more info.
+        """)
+    }
+    guard !notes.isEmpty else { return }
+    log.note("Caveats:")
+    for note in notes {
+      for line in note.components(separatedBy: .newlines) {
+        log.note(line)
+      }
+    }
+  }
+
+  func generate() async throws {
+    let buildDirPath = buildDir.absoluteInWorkingDir.resolvingSymlinks
+    log.info("Generating project for '\(buildDirPath)'...")
+
     let projectRootDir = self.projectRootDir?.absoluteInWorkingDir
     let buildDir = try NinjaBuildDir(at: buildDirPath, projectRootDir: projectRootDir)
     let outputDir = miscOptions.outputDir?.absoluteInWorkingDir ?? buildDir.projectRootDir
@@ -350,6 +370,7 @@ struct SwiftXcodegen: AsyncParsableCommand, Sendable {
         try lldbLLVMWorkspace.write("LLDB+LLVM", into: outputDir)
       }
     }
+    showCaveatsIfNeeded()
   }
 
   func run() async {