Deprecate --use-integrated-swift-driver option (#9334)

The Native Build system supports a `--use-integrated-swift-driver`
command line argument. The feature is not fully funtional. With the
transition to SwiftBuild, mark this option as deprecated.

Fixes: #9323
Issue: rdar://163962023

Author: bkhouri

Sources/CoreCommands/Options.swift

@@ -526,6 +526,7 @@ public struct BuildOptions: ParsableArguments {
     /// Whether to use the integrated Swift driver rather than shelling out
     /// to a separate process.
     @Flag()
+    /// This flag is deprecated but cannot indicate so in Swift Argument Parser until https://github.com/apple/swift-argument-parser/issues/656
     public var useIntegratedSwiftDriver: Bool = false
 
     /// A flag that indicates this build should check whether targets only import

Sources/CoreCommands/SwiftCommandState.swift

@@ -854,6 +854,11 @@ public final class SwiftCommandState {
         observabilityScope: ObservabilityScope? = .none,
         delegate: BuildSystemDelegate? = nil
     ) async throws -> BuildSystem {
+
+        if self.options.build.useIntegratedSwiftDriver && self.options.build.buildSystem == .native {
+            self.observabilityScope.emit(warning: "`--use-integrated-swift-driver` option is deprecated as the feature is not fully functional.")
+        }
+
         guard let buildSystemProvider else {
             fatalError("build system provider not initialized")
         }