[xcodegen] Avoid emitting Swift Obj-C header

This isn't needed currently and works around
an assertion failure.

Author: hamishknight

utils/swift-xcodegen/Sources/SwiftXcodeGen/Generator/ProjectGenerator.swift

@@ -558,6 +558,13 @@ fileprivate final class ProjectGenerator {
       buildSettings.common.DEFINES_MODULE = "YES"
     }
 
+    // Disable the Obj-C bridging header; we don't currently use this, and
+    // even if we did, we'd probably want to use the one in the Ninja build
+    // folder.
+    // This also works around a compiler crash
+    // (https://github.com/swiftlang/swift/issues/78190).
+    buildSettings.common.SWIFT_OBJC_INTERFACE_HEADER_NAME = ""
+
     if let last = buildArgs.takeFlagGroup(.O, .Onone) {
       buildSettings.common.SWIFT_OPTIMIZATION_LEVEL = last.printed
     }

utils/swift-xcodegen/Sources/Xcodeproj/XcodeProjectModel.swift

@@ -441,6 +441,7 @@ public struct Xcode {
       public var SWIFT_FORCE_DYNAMIC_LINK_STDLIB: String?
       public var SWIFT_INCLUDE_PATHS: [String]?
       public var SWIFT_MODULE_ALIASES: [String: String]?
+      public var SWIFT_OBJC_INTERFACE_HEADER_NAME: String?
       public var SWIFT_OPTIMIZATION_LEVEL: String?
       public var SWIFT_VERSION: String?
       public var TARGET_NAME: String?