[CMake] Fix creation of swiftmodule directories on Apple platforms

The way it was set up before worked for Ninja but not for Xcode, due
to me not listing the swiftmodule directories as actual outputs of the
create-directories target. The resulting fix here is actually simpler
and involves fewer processes anyway, so good for us.

https://bugs.swift.org/browse/SR-10029

Author: jrose-apple

cmake/modules/SwiftSource.cmake

@@ -283,17 +283,10 @@ function(_compile_swift_files
 
   list(APPEND swift_flags ${SWIFTFILE_FLAGS})
 
-  set(obj_dirs)
+  set(dirs_to_create)
   foreach(output ${SWIFTFILE_OUTPUT})
     get_filename_component(objdir "${output}" PATH)
-    list(APPEND obj_dirs "${objdir}")
-  endforeach()
-  list(REMOVE_DUPLICATES obj_dirs)
-
-  set(command_create_dirs)
-  foreach(objdir ${obj_dirs})
-    list(APPEND command_create_dirs
-      COMMAND "${CMAKE_COMMAND}" -E make_directory "${objdir}")
+    list(APPEND dirs_to_create "${objdir}")
   endforeach()
 
   set(module_file)
@@ -333,11 +326,9 @@ function(_compile_swift_files
     endif()
 
     if(SWIFTFILE_SDK IN_LIST SWIFT_APPLE_PLATFORMS)
-      list(APPEND command_create_dirs
-          COMMAND "${CMAKE_COMMAND}" -E make_directory "${specific_module_dir}")
+      list(APPEND dirs_to_create "${specific_module_dir}")
     else()
-      list(APPEND command_create_dirs
-          COMMAND "${CMAKE_COMMAND}" -E make_directory "${module_dir}")
+      list(APPEND dirs_to_create "${module_dir}")
     endif()
 
     # If we have extra regexp flags, check if we match any of the regexps. If so
@@ -398,7 +389,7 @@ function(_compile_swift_files
   endif()
 
   if (SWIFT_REPORT_STATISTICS)
-    list(GET obj_dirs 0 first_obj_dir)
+    list(GET dirs_to_create 0 first_obj_dir)
     list(APPEND swift_flags "-stats-output-dir" ${first_obj_dir})
   endif()
 
@@ -433,12 +424,12 @@ function(_compile_swift_files
   endif()
 
   # First generate the obj dirs
+  list(REMOVE_DUPLICATES dirs_to_create)
   add_custom_command_target(
-      obj_dirs_dependency_target
-      ${command_create_dirs}
-      COMMAND ""
-      OUTPUT ${obj_dirs}
-      COMMENT "Generating obj dirs for ${first_output}")
+      create_dirs_dependency_target
+      COMMAND "${CMAKE_COMMAND}" -E make_directory ${dirs_to_create}
+      OUTPUT ${dirs_to_create}
+      COMMENT "Generating dirs for ${first_output}")
 
   # Then we can compile both the object files and the swiftmodule files
   # in parallel in this target for the object file, and ...
@@ -478,7 +469,7 @@ function(_compile_swift_files
         ${swift_compiler_tool_dep}
         ${file_path} ${source_files} ${SWIFTFILE_DEPENDS}
         ${swift_ide_test_dependency}
-        ${obj_dirs_dependency_target}
+        ${create_dirs_dependency_target}
         ${copy_legacy_layouts_dep}
       COMMENT "Compiling ${first_output}")
   set("${dependency_target_out_var_name}" "${dependency_target}" PARENT_SCOPE)
@@ -513,7 +504,7 @@ function(_compile_swift_files
           ${swift_compiler_tool_dep}
           ${source_files} ${SWIFTFILE_DEPENDS}
           ${swift_ide_test_dependency}
-          ${obj_dirs_dependency_target}
+          ${create_dirs_dependency_target}
         COMMENT "Generating ${module_file}")
     set("${dependency_module_target_out_var_name}" "${module_dependency_target}" PARENT_SCOPE)
 
@@ -529,7 +520,7 @@ function(_compile_swift_files
         DEPENDS
           ${swift_compiler_tool_dep}
           ${source_files} ${SWIFTFILE_DEPENDS}
-          ${obj_dirs_dependency_target}
+          ${create_dirs_dependency_target}
         COMMENT "Generating ${sib_file}"
         EXCLUDE_FROM_ALL)
     set("${dependency_sib_target_out_var_name}" "${sib_dependency_target}" PARENT_SCOPE)
@@ -545,7 +536,7 @@ function(_compile_swift_files
         DEPENDS
           ${swift_compiler_tool_dep}
           ${source_files} ${SWIFTFILE_DEPENDS}
-          ${obj_dirs_dependency_target}
+          ${create_dirs_dependency_target}
         COMMENT "Generating ${sibopt_file}"
         EXCLUDE_FROM_ALL)
     set("${dependency_sibopt_target_out_var_name}" "${sibopt_dependency_target}" PARENT_SCOPE)
@@ -562,7 +553,7 @@ function(_compile_swift_files
         DEPENDS
           ${swift_compiler_tool_dep}
           ${source_files} ${SWIFTFILE_DEPENDS}
-          ${obj_dirs_dependency_target}
+          ${create_dirs_dependency_target}
           COMMENT "Generating ${sibgen_file}"
           EXCLUDE_FROM_ALL)
     set("${dependency_sibgen_target_out_var_name}" "${sibgen_dependency_target}" PARENT_SCOPE)