- Don't hardcode -O3 and respect the CXXFLAGS
- Don't pass -ldl to the linker

Index: src/CMakeLists.txt
--- src/CMakeLists.txt.orig
+++ src/CMakeLists.txt
@@ -264,7 +264,7 @@ if (NOT MSVC)
     set(CMAKE_CXX_FLAGS                "-Wall -Wextra -std=c++11 ${CMAKE_CXX_FLAGS}")
     set(CMAKE_CXX_FLAGS_DEBUG          "-g3 ${CMAKE_CXX_FLAGS_DEBUG}")
     set(CMAKE_CXX_FLAGS_MINSIZEREL     "-Os ${CMAKE_CXX_FLAGS_MINSIZEREL}")
-    set(CMAKE_CXX_FLAGS_RELEASE        "-O3 ${CMAKE_CXX_FLAGS_RELEASE}")
+    set(CMAKE_CXX_FLAGS_RELEASE        "${CMAKE_CXX_FLAGS_RELEASE} ${CXXFLAGS}")
     set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O2 -g3 ${CMAKE_CXX_FLAGS_RELWITHDEBINFO}")
 elseif (MULTI_THREAD)
     set(CMAKE_CXX_FLAGS_DEBUG          "/MTd ${CMAKE_CXX_FLAGS_DEBUG}")