Merge pull request #173 from YosysHQ/gatecat/ecp5-add-dcs libtrellis: Add DCS bels

diff --git a/libtrellis/CMakeLists.txt b/libtrellis/CMakeLists.txt
index 21b2ace..05d41ba 100644
--- a/libtrellis/CMakeLists.txt
+++ b/libtrellis/CMakeLists.txt

@@ -37,6 +37,7 @@
         -DBOOST_SP_NO_ATOMIC_ACCESS
         -DBOOST_AC_DISABLE_THREADS
         -DBOOST_NO_CXX11_HDR_MUTEX
+        -DBOOST_NO_CXX11_HDR_ATOMIC
     )
 else()
     set(USE_THREADS ON)