somehow need to set CMAKE_CXX_FLAGS here again

Index: tools/pr-downloader/src/CMakeLists.txt
--- tools/pr-downloader/src/CMakeLists.txt.orig
+++ tools/pr-downloader/src/CMakeLists.txt
@@ -5,6 +5,8 @@ if(WIN32)
     endif()
 endif()
 
+set(CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
+
 add_library(pr-downloader
     Downloader/CurlWrapper.cpp
     Downloader/Download.cpp
