$ ./b2 cxxflags='-std=gnu++11 -D__USE_W32_SOCKETS -D"__MASABI_LONG(x)=(x)" -fpermissive'
..
gcc.compile.c++ bin.v2/libs/thread/build/gcc-11/release/threading-multi/pthread/once.o
libs\thread\src\pthread\once.cpp:8:10: fatal error: ./once_atomic.cpp: No such file or directory
    8 | #include "./once_atomic.cpp"
      |          ^~~~~~~~~~~~~~~~~~~
compilation terminated.

    
gcc.compile.c++ bin.v2/libs/date_time/build/gcc-11/release/threading-multi/gregorian/greg_month.o
libs\date_time\src\gregorian\greg_month.cpp:26:10: fatal error: greg_names.hpp: No such file or directory
   26 | #include "greg_names.hpp"
      |          ^~~~~~~~~~~~~~~~
compilation terminated.

The compile error "greg_names.hpp: No such file or directory" is very odd, the header file greg_names.hpp actually is in libs\date_time\src\gregorian, same directory as greg_month.cpp Same problem is for once_atomic.cpp..

What can I do?