Pass the correct compiler flag for CoreDiagnostics. (#3312)

* Pass the correct compiler flag for CoreDiagnostics.

When CoreDiagnostics is open sourced, we'll need to ensure that the
right compiler flag is passed. This doesn't add support for Carthage yet
but allows the frameworkbuilder to pass the flag for carthage as well.
An update to the zipbuilder to allow for carthage will follow shortly.

* Remove accidental change.

ZipBuilder/Sources/ZipBuilder/FrameworkBuilder.swift

@@ -55,14 +55,18 @@ struct FrameworkBuilder {
   /// The directory containing the Xcode project and Pods folder.
   private let projectDir: URL
 
+  /// A flag to indicate this build is for carthage. This is primarily used for CoreDiagnostics.
+  private let carthageBuild: Bool
+
   /// The Pods directory for building the framework.
   private var podsDir: URL {
     return projectDir.appendingPathComponent("Pods", isDirectory: true)
   }
 
   /// Default initializer.
-  init(projectDir: URL) {
+  init(projectDir: URL, carthageBuild: Bool = false) {
     self.projectDir = projectDir
+    self.carthageBuild = carthageBuild
   }
 
   // MARK: - Public Functions
@@ -223,7 +227,8 @@ struct FrameworkBuilder {
                            "ARCHS=\(arch.rawValue)",
                            "BUILD_DIR=\(buildDir.path)",
                            "-sdk", platform.rawValue]
-    let args = standardOptions + platform.extraArguments()
+    let distributionFlag = carthageBuild ? "-DFIREBASE_BUILD_CARTHAGE" : "-DFIREBASE_BUILD_ZIP_FILE"
+    let args = standardOptions + platform.extraArguments() + [distributionFlag]
     print("""
     Compiling \(framework) for \(arch.rawValue) with command:
     /usr/bin/xcodebuild \(args.joined(separator: " "))

ZipBuilder/Sources/ZipBuilder/ZipBuilder.swift

@@ -661,7 +661,8 @@ struct ZipBuilder {
   /// .framework file already).
   private func generateFrameworks(fromPods pods: [CocoaPodUtils.PodInfo],
                                   inProjectDir projectDir: URL,
-                                  useCache: Bool = false) -> [String: [URL]] {
+                                  useCache: Bool = false,
+                                  carthageBuild: Bool = false) -> [String: [URL]] {
     // Verify the Pods folder exists and we can get the contents of it.
     let fileManager = FileManager.default