[Plugins] Build and install _CompilerPluginSupport module directory.

Fix the generated layout for the `_CompilerPluginSupport` Swift module,
so that properly-named Swift interfaces are placed within a
`.swiftmodule` subdirectory. Install that directory into lib/swift.

Author: DougGregor

lib/CompilerPluginSupport/CMakeLists.txt

@@ -26,15 +26,36 @@ if(SWIFT_SWIFT_PARSER)
     set(DEPLOYMENT_VERSION ${SWIFT_ANDROID_API_LEVEL})
   endif()
 
+  # Determine the Swift module path
+  set(module_triple ${SWIFT_SDK_${SWIFT_HOST_VARIANT_SDK}_ARCH_${SWIFT_HOST_VARIANT_ARCH}_MODULE})
+  set(module_dir "${CMAKE_LIBRARY_OUTPUT_DIRECTORY}")
+  set(module_base "${module_dir}/${module_name}.swiftmodule")
+  set(module_file "${module_base}/${module_triple}.swiftmodule")
+  set(module_interface_file "${module_base}/${module_triple}.swiftinterface")
+  set(module_doc_file "${module_base}/${module_triple}.swiftdoc")
+
   get_target_triple(target target_variant "${SWIFT_HOST_VARIANT_SDK}" "${SWIFT_HOST_VARIANT_ARCH}"
     MACCATALYST_BUILD_FLAVOR ""
     DEPLOYMENT_VERSION "${DEPLOYMENT_VERSION}")
 
+  # Add a custom target to create the module directory.
+  add_custom_command_target(
+      create_module_dirs_dependency_target
+      COMMAND "${CMAKE_COMMAND}" -E make_directory ${module_base}
+      OUTPUT ${module_base}
+      COMMENT "Generating module directory for ${module_name}")
+  add_dependencies(${library_name} ${create_module_dirs_dependency_target})
+
+  # Build the module with library evolution enabled and install into the
+  # appropriate locations.
   target_compile_options("${library_name}" PRIVATE
     $<$<COMPILE_LANGUAGE:Swift>:
       -module-name;${module_name};
       -enable-library-evolution;
-      -emit-module-interface;
+      -emit-module-path;
+      "${module_file}";
+      -emit-module-interface-path;
+      "${module_interface_file}";
       -target;${target}>)
 
   target_link_libraries("${library_name}"
@@ -56,4 +77,7 @@ if(SWIFT_SWIFT_PARSER)
       DESTINATION "lib${LLVM_LIBDIR_SUFFIX}"
       COMPONENT compiler)
 
+    swift_install_in_component(DIRECTORY "${module_base}"
+                               DESTINATION "lib${LLVM_LIBDIR_SUFFIX}/swift"
+                               COMPONENT compiler)
 endif()