fcntl(SETLKW) fails on standard streams

[dmik]

LIBCx replaces the LIBC implementation of fcntl(SETLKW) and friends which uses DosSetFileLocks because the latter does not guarantee atomicity of lock/unlock operations in many cases (like overlapping lock regions etc.) and does not have deadlock detection. However, the current LIBCx implementation only supports regular files (i.e. files which have a valid path that is used as a key). Neither standard I/O streams nor pipes nor sockets are not supported (and fcntl(SETLKW) will return EINVAL on them) .

It is possible to make up unique keys for stdio streams and pipes (and even sockets) and make them work too but it requires some coding and testing. One case where we found it failing is this: bitwiseworks/kbuild-os2#5.