[scudo][standalone] Link tests against libatomic
[scudo][standalone] Link tests against libatomic

Summary:
Some clang versions (< 6.0) do not inline the atomic builtin functions
leaving unresolved references to `__atomic_load_8` and so on (seems to
be mostly 64-bit atomics on 32-bit platforms).
I tried without success to use some cmake magic to detect when that
would be the case, and decided to fall back to unconditionally
linking libatomic.

Reviewers: morehouse, eugenis, vitalybuka, hctim, tejohnson

Reviewed By: tejohnson

Subscribers: mgorny, delcypher, jfb, #sanitizers, llvm-commits

Tags: #llvm, #sanitizers

Differential Revision: https://reviews.llvm.org/D64134

git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@365052 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt