valgrind: Update to version 3.18.1

valgrind: Update to version 3.18.1

This version has some improvements for musl.
This version works fine for me on MIPS 32 BE without MIPS16 even on musl.

The additional patch is needed to make valgrind use the correct syscall
numbers for new syscalls like clock_gettime64. The MIPS architecture
uses special syscall ranges which are different from most other systems.
The patch is pending upstream: https://bugs.kde.org/show_bug.cgi?id=444781

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>