[CMake] Fix creation of swiftmodule directories on Apple platforms (2)

The previous commit resulted in multiple targets that claimed to be
able to generate the directories in question. Instead, just create the
directories as a pre-build step for the targets that actually need
them. (This does keep the cleanup for the existing directory creation
target, though.)

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

Author: jrose-apple

cmake/modules/SwiftSource.cmake

@@ -195,6 +195,7 @@ function(_compile_swift_files
 
   # Compute flags for the Swift compiler.
   set(swift_flags)
+  set(swift_module_flags)
 
   _add_variant_swift_compile_flags(
       "${SWIFTFILE_SDK}"
@@ -309,6 +310,8 @@ function(_compile_swift_files
     if(SWIFTFILE_SDK IN_LIST SWIFT_APPLE_PLATFORMS)
       set(specific_module_dir "${module_base}.swiftmodule")
       set(module_base "${module_base}.swiftmodule/${SWIFTFILE_ARCHITECTURE}")
+    else()
+      set(specific_module_dir)
     endif()
     set(module_file "${module_base}.swiftmodule")
     set(module_doc_file "${module_base}.swiftdoc")
@@ -321,14 +324,8 @@ function(_compile_swift_files
 
     if(SWIFT_ENABLE_PARSEABLE_MODULE_INTERFACES)
       set(interface_file "${module_base}.swiftinterface")
-      list(APPEND swift_flags
-          "-emit-parseable-module-interface-path" "${interface_file}")
-    endif()
-
-    if(SWIFTFILE_SDK IN_LIST SWIFT_APPLE_PLATFORMS)
-      list(APPEND dirs_to_create "${specific_module_dir}")
-    else()
-      list(APPEND dirs_to_create "${module_dir}")
+      list(APPEND swift_module_flags
+           "-emit-parseable-module-interface-path" "${interface_file}")
     endif()
 
     # If we have extra regexp flags, check if we match any of the regexps. If so
@@ -494,10 +491,13 @@ function(_compile_swift_files
         module_dependency_target
         COMMAND
           "${CMAKE_COMMAND}" "-E" "remove" "-f" ${module_outputs}
+        COMMAND
+          "${CMAKE_COMMAND}" "-E" "make_directory" ${module_dir}
+          ${specific_module_dir}
         COMMAND
           "${PYTHON_EXECUTABLE}" "${line_directive_tool}" "@${file_path}" --
           "${swift_compiler_tool}" "-emit-module" "-o" "${module_file}"
-          ${swift_flags} "@${file_path}"
+          ${swift_flags} ${swift_module_flags} "@${file_path}"
         ${command_touch_module_outputs}
         OUTPUT ${module_outputs}
         DEPENDS