Fix compile on Windows + MSYS2-MinGW64 (MaskRay#46)

1. libClangDriver.a shipped by MSYS2 needs -lversion which is not
   included in CMAKE_CXX_STANDARD_LIBRARIES by default.
2. Use string literal for DEFAULT_RESOURCE_DIRECTORY to support
   backslashes in path.

CMakeLists.txt

@@ -124,7 +124,7 @@ endif()
 ### Definitions
 
 target_compile_definitions(ccls PRIVATE
-                           DEFAULT_RESOURCE_DIRECTORY="${Clang_RESOURCE_DIR}")
+                           DEFAULT_RESOURCE_DIRECTORY=R"\(${Clang_RESOURCE_DIR}\)")
 
 ### Includes
 

cmake/FindClang.cmake

@@ -137,4 +137,7 @@ if(Clang_FOUND AND NOT TARGET Clang::Clang)
   find_package(Curses REQUIRED)
   find_package(ZLIB REQUIRED)
   set_property(TARGET Clang::Clang PROPERTY IMPORTED_LINK_INTERFACE_LIBRARIES "${_Clang_LIBRARIES};${CURSES_LIBRARIES};${ZLIB_LIBRARIES}")
+  if(MINGW)
+    set_property(TARGET Clang::Clang APPEND_STRING PROPERTY IMPORTED_LINK_INTERFACE_LIBRARIES ";version")
+  endif()
 endif()