Use LTP for testing valgrind

Use LTP for testing valgrind

Add a new top level make target ltpchecks which will fetch the latest
linux test project (ltp) release as defined by the LTP_VERSION and
LTP_SHA256 variables in auxprogs/Makefile.am (update those when a new
version of ltp is released). If the ltp tar.xz has already been
downloaded, or it has already been unpacked and build, the (cached)
file and build will be reused.

The actual testing is done through the auxprogs/ltp-tester.sh script.
It takes all executable tests from the ltp testcases under
kernel/syscalls and runs them 3 times. Once directly, not under
valgrind, once with -q --tool=none and once with -q
--tool=memcheck. It then checks that valgrind didn't produce any
messages with the none tool, that there were no fatal errors produced
(as defined in auxprogs/ltp-error-patterns.txt) and that the ltp
results are the same with and without valgrind.

Currently there are 1472 test binaries and running them all (serially)
takes more than three hours and detects various missing or incomplete
syscall handlers in valgrind, plus various crashers.

https://bugs.kde.org/show_bug.cgi?id=502679