Update from https://crrev.com/329939

tools/clang/blink_gc_plugin/CMakeLists.txt

-# This line is read by update.sh and other scripts in tools/clang/scripts
-# Note: The spaces are significant.
 set(LIBRARYNAME BlinkGCPlugin)
 
-add_llvm_loadable_module("lib${LIBRARYNAME}"
-                         BlinkGCPlugin.cpp
-                         Edge.cpp
-                         RecordInfo.cpp
-                        )
+set(plugin_sources
+  BlinkGCPlugin.cpp
+  Edge.cpp
+  RecordInfo.cpp)
 
-add_dependencies("lib${LIBRARYNAME}" clang)
+if(WIN32)
+  # Clang doesn't support loadable modules on Windows. Unfortunately, building
+  # the plugin as a static library and linking clang against it doesn't work.
+  # Since clang doesn't reference any symbols in our static library, the linker
+  # strips it out completely.
+  # Instead, we rely on the fact that the SOURCES property of a target is no
+  # read-only after CMake 3.1 and use it to compile the plugin directly into
+  # clang...
+  cmake_minimum_required(VERSION 3.1)
+  # Paths must be absolute, since we're modifying a target in another directory.
+  set(absolute_sources "")
+  foreach(source ${plugin_sources})
+    list(APPEND absolute_sources ${CMAKE_CURRENT_SOURCE_DIR}/${source})
+  endforeach()
+  set_property(TARGET clang APPEND PROPERTY SOURCES ${absolute_sources})
 
-cr_install(TARGETS "lib${LIBRARYNAME}" LIBRARY DESTINATION lib)
+  cr_add_test(blink_gc_plugin_test
+    python
+    ${CMAKE_CURRENT_SOURCE_DIR}/tests/test.py
+    ${CMAKE_BINARY_DIR}/bin/clang
+    )
+else()
+  add_llvm_loadable_module("lib${LIBRARYNAME}" ${plugin_sources})
+  add_dependencies("lib${LIBRARYNAME}" clang)
 
-cr_add_test(blink_gc_plugin_test
-  ${CMAKE_CURRENT_SOURCE_DIR}/tests/test.sh
-  ${CMAKE_BINARY_DIR}/bin/clang
-  $<TARGET_FILE:lib${LIBRARYNAME}>
-  )
+  cr_install(TARGETS "lib${LIBRARYNAME}" LIBRARY DESTINATION lib)
+
+  cr_add_test(blink_gc_plugin_test
+    python
+    ${CMAKE_CURRENT_SOURCE_DIR}/tests/test.py
+    ${CMAKE_BINARY_DIR}/bin/clang
+    $<TARGET_FILE:lib${LIBRARYNAME}>
+    )
+endif()