[VxWorks] Support for Posix pipes

Currently Qt uses VxWorks PipeDrv, which doesn't end up cleaning the created pipes on exit or restart, so there is a need to have the Posix pipe support, including the QTBUG-106117 workaround.

The following 5.15 changes need to be added to 6.x sources too:

https://codereview.qt-project.org/gitweb?p=qt/tqtc-qtbase.git;a=commit;h=17ce0b879f256677bad9d9c471a7986b54d65d68

https://codereview.qt-project.org/gitweb?p=qt/tqtc-qtbase.git;a=commit;h=ceea1bc43660aaf53ed8f10c0ee13df9018dd353

https://codereview.qt-project.org/gitweb?p=qt/tqtc-qtbase.git;a=commit;h=215396d4aab101e2c9beff224bfb5c27daa3afcd

https://codereview.qt-project.org/gitweb?p=qt/tqtc-qtbase.git;a=commit;h=420e6aa5aa7c547b6ef4615d9c60f9031689f59c

https://codereview.qt-project.org/gitweb?p=qt/tqtc-qtbase.git;a=commit;h=695897ac4691724e573eb68f0a5e230c6b614fb1