(( PLEASE MERGE TO STABLE ))

Linker.c: linux/ppc: We call mmap() to allocate additional pages to
                     create jump islands.  In the case where no
                     additional memory was needed the mmap call was
                     being made with a size of 0 which would fail.
                     The call is now conditionalised and documentation
                     has been added to the code.  Closes trac #439.