Add "thirdparty" into the "find_path" search paths

Please only merge the CMakeLists.txt file.
Will this replace these two additional variables I set in vcbuild.bat and Unix Makefiles?

-DCMAKE_INCLUDE_PATH="$(RIME_ROOT)/thirdparty/include"
-DCMAKE_LIBRARY_PATH="$(RIME_ROOT)/thirdparty/lib"