Add types and constants for Linux/PPC64.

Adds types and constants for Linux/PPC64 to changed modules.
Add Linux/PPC64 values to core.sys.posix.fcntl.

Simply adds the missing values.
Add ucontext_t on Linux/PPC64.

Adds the required data structures for ucontext_t.
Fix O_RSYNC value on Linux/PPC64
Implement review comments to ucontext on Linux/PPC64
Implement fibers on Linux/PPC64.

As a first attempt I am using the Posix version with ucontext_t.
Partial fix to compile on X86
Final fix for X86