This file is essentially clang-linux.jam with changes for clang on Windows in gcc/mingw target mode, which should also use clang-linux.jam. The changes are simply that multithreading should use the -pthread option rather than the -mthreads option on Windows. I could have directly updated clang-linux.jam, since the change only affects clang targeted to Windows but I am being conservative and showing the change in this file for others to look at first.