MinGW support (from cameron314 in #3)

Author: preshing

cmake/BuildSettings.cmake

@@ -3,7 +3,7 @@ if(${MSVC})
     set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} /Zi")
     set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} /Zi")
     set(CMAKE_EXE_LINKER_FLAGS_RELEASE "${CMAKE_EXE_LINKER_FLAGS_RELEASE} /debug")
-elseif(${UNIX})
+else()
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
     if(${CYGWIN})   # Don't specify -pthread on Cygwin
     else()