Adapts __ppc_get_timebase to the upcoming GCC 4.8 that provides
__builtin_ppc_get_timebase. Building applicationns with previous
versions of GCC will continue to use the internal implementation.
[BZ #13743]
A new class of installed headers has been documented for low-level
platform-specific functionality. PowerPC added the first instance with a
function to provide time base register access (__ppc_get_timebase). This
is required for applications that measure time at high frequencies with
high precision that can't afford a syscall.
