Build the Clang plugin on Windows.

tools/clang/plugins/CMakeLists.txt

Index: tools/clang/plugins/CMakeLists.txt
diff --git a/tools/clang/plugins/CMakeLists.txt b/tools/clang/plugins/CMakeLists.txt
index d17de19fcd09d79a5a41860469a9dd97a557f29a..e4eea86c7bf1f1675310cd1bb97678fd7b0e8a1b 100644
--- a/tools/clang/plugins/CMakeLists.txt
+++ b/tools/clang/plugins/CMakeLists.txt
@@ -1,15 +1,33 @@
-add_llvm_loadable_module(libFindBadConstructs
-                         ChromeClassTester.cpp
-                         FindBadConstructsAction.cpp
-                         FindBadConstructsConsumer.cpp
-                        )
+set(plugin_sources
+  ChromeClassTester.cpp
+  FindBadConstructsAction.cpp
+  FindBadConstructsConsumer.cpp)
 
-add_dependencies(libFindBadConstructs 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})
+else()
+  add_llvm_loadable_module(libFindBadConstructs ${plugin_sources})
+  add_dependencies(libFindBadConstructs clang)
 
-cr_install(TARGETS libFindBadConstructs LIBRARY DESTINATION lib)
+  cr_install(TARGETS libFindBadConstructs LIBRARY DESTINATION lib)
 
-cr_add_test(plugins_test
-  ${CMAKE_CURRENT_SOURCE_DIR}/tests/test.sh
-  ${CMAKE_BINARY_DIR}/bin/clang
-  $<TARGET_FILE:libFindBadConstructs>
-  )
+  # TODO(dcheng): Rewrite the test framework so it works on Windows too.
+  cr_add_test(plugins_test
+    ${CMAKE_CURRENT_SOURCE_DIR}/tests/test.sh
+    ${CMAKE_BINARY_DIR}/bin/clang
+    $<TARGET_FILE:libFindBadConstructs>
+    )
+endif()