[asan] make heavy_uar_test a bit more heavy and fix he fake stack to pass this test

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@179286 91177308-0d34-0410-b5e6-96231b3b80d8
[sanitizer] Syscall hooks.

Pre- and post- hooks for linux syscalls. Not wired into anything, but exposed
through public interface.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@179288 91177308-0d34-0410-b5e6-96231b3b80d8