cmake HAVE_DECLSPEC_THREAD examples

mmp/pbrt-v3 CMakeLists.txt :272 

CHECK_CXX_SOURCE_COMPILES ( "
__declspec(thread) int x; int main() { }
" HAVE_DECLSPEC_THREAD )

mmp/pbrt-v3 CMakeLists.txt :284 

ELSEIF ( HAVE_DECLSPEC_THREAD )