valgrind: add patch to fix build on PowerPC uClibc

uClibc on PowerPC forgot to define some PTRACE_* definitions. Even
though the Buildroot uClibc package has a fix for this, it doesn't fix
external uClibc toolchains that are not patched. Therefore this commit
adds a patch to Valgrind to workaround the problem by defining
PTRACE_GETSIGINFO to the appropriate value on PowerPC when it's not
defined by the C library.

Fixes:

  http://autobuild.buildroot.org/results/bc6/bc6be9aa1ad39201a1045a65c0c3eb1e968371f2/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>