This feature was already implemented in the LLVM OpenMP runtime, so we are only modifying CLANG in this revision.
The value used to identify a mutexinoutset dep-type in the LLVM OpenMP runtime is 4.
I had to adapt some tests because they were relying on an error message that changed with the introduction of this new dep-type. Apart from those, I also modified test/OpenMP/task_codegen.cpp to test that we emit the right code.