Add Linux/PPC64 values to core.sys.posix.fcntl.

Simply adds the missing values.
Merge pull request #502 from redstar/ppc_fcntl

Add Linux/PPC64 values to core.sys.posix.fcntl.
Add ucontext_t on Linux/PPC64.

Adds the required data structures for ucontext_t.
Merge pull request #503 from redstar/ppc_ucontext

Add ucontext_t on Linux/PPC64.
Fix O_RSYNC value on Linux/PPC64
Merge pull request #504 from redstar/ppc_fcntl

Fix O_RSYNC value on Linux/PPC64