Make force_lib.c --xcode specific.

Author: johnno1962

SwiftCompilerSources/CMakeLists.txt

@@ -171,7 +171,14 @@ function(add_swift_compiler_modules_library name)
   endforeach()
 
   # Create a static library containing all module object files.
-  add_library(${name} STATIC force_lib.c ${all_obj_files})
+  if (XCODE)
+    # Xcode does not compile libraries that contain only object files.
+    # Therefore, it fails to create the static library. As a workaround,
+    # we add an empty source file force_lib.c to the target.
+    add_library(${name} STATIC force_lib.c ${all_obj_files})
+  else()
+    add_library(${name} STATIC ${all_obj_files})
+  endif()
   add_dependencies(${name} ${all_module_targets})
   set_target_properties(${name} PROPERTIES LINKER_LANGUAGE CXX)
   set_property(GLOBAL APPEND PROPERTY SWIFT_BUILDTREE_EXPORTS ${name})

SwiftCompilerSources/force_lib.c

@@ -10,5 +10,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-/// Dummy source file to force CMake generated SwiftInTheCompiler.xcodeproj to sucessfully build static
-/// libraries containing only object fies for "bootstrap" process building Swift sources into compiler.
+/// Dummy source file to force CMake generated SwiftInTheCompiler.xcodeproj
+/// to sucessfully build static libraries conatining only object files used
+/// during "bootstrap" process to link Swift sources into the compiler.