Copy all of the swift-syntax Swift modules.

Make the build directory for lib/swift/host look like the eventually
toolchain directory by copying in all of the Swift module files. This
makes it easier to correctly build anything requiring these libraries
against either the build or the install directories.

Author: DougGregor

lib/ASTGen/CMakeLists.txt

@@ -114,8 +114,24 @@ if (SWIFT_SWIFT_PARSER)
     )
   endforeach()
 
+  # Copy all of the Swift modules from earlyswiftsyntax so they can be found
+  # in the same relative place within the build directory as in the final
+  # toolchain.
+  list(TRANSFORM SWIFT_SYNTAX_MODULES APPEND ".swiftmodule"
+       OUTPUT_VARIABLE SWIFT_SYNTAX_MODULE_DIRS)
+  foreach(module_dir ${SWIFT_SYNTAX_MODULE_DIRS})
+    file(GLOB module_files
+         "${SWIFT_SYNTAX_LIBRARIES_SOURCE_DIR}/${module_dir}/*.swift*")
+    add_custom_command(
+      TARGET swiftASTGen PRE_BUILD
+      COMMAND ${CMAKE_COMMAND} -E make_directory ${SWIFT_SYNTAX_LIBRARIES_DEST_DIR}/${module_dir}
+      COMMAND ${CMAKE_COMMAND} -E copy_if_different ${module_files} ${SWIFT_SYNTAX_LIBRARIES_DEST_DIR}/${module_dir}/
+      COMMENT "Copying ${module_dir}"
+    )
+  endforeach()
+
   target_include_directories(swiftASTGen PUBLIC
-    "${SWIFT_PATH_TO_EARLYSWIFTSYNTAX_BUILD_DIR}/lib/swift/host")
+    ${SWIFT_SYNTAX_LIBRARIES_DEST_DIR})
 
   set_property(GLOBAL APPEND PROPERTY SWIFT_EXPORTS swiftASTGen)
 endif()