Fixed the use of addr2line to discover the separator symbol.

In systems where addr2line has a version greater than 2.22 pprof fails
in discover the separator symbol (_fini). This patch identifies if
addr2line can find the symbol, otherwise pprof uses objdump to recover
a address that addr2line's newer versions can recognize as the separator
function.
Fixed the way that pprof packed profile data in BE.

pprof was writing profile data in a way that only works for little-endian
files, this patch verifies if the system is big-endian and writes packed
data correctly.
Fixed issues with heap checker on PPC64 LE.

Fixed the wrapper for the syscall sys_clone and the test for heap
checker on PPC64 LE. Both use the ODP structure, which is only
used on BE architectures.
VDSOsupport cleanup

This patch cleans up unused VDSO getcpu racking from VDSOsupport class,
since the code is not used anywhere in gperftools and symbol name is not
architecture independent.
PowerPC: stacktrace function refactor and fixes

This patch fixes the stacktrace creating when the function is
interrupted by a signal. For Linux, the vDSO signal trampoline symbol is
compared against LR from stack backchain and handled different in that
case (since the signal trampoline layout a different stack frame).

Because of this extensive change the PowerPC stacktrace code has now
been refactored to split in Linux and Darwin specific codes.