[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

llvm-svn: 365052

compiler-rt/lib/scudo/standalone/tests/CMakeLists.txt

@@ -23,6 +23,8 @@ foreach(lib ${SANITIZER_TEST_CXX_LIBRARIES})
   list(APPEND LINK_FLAGS -l${lib})
 endforeach()
 list(APPEND LINK_FLAGS -pthread)
+# Linking against libatomic is required with some compilers
+list(APPEND LINK_FLAGS -latomic)
 
 set(SCUDO_TEST_HEADERS)
 foreach (header ${SCUDO_HEADERS})