XCode 7 Link Errors for Simulator "Building for iOS simulator, but linking in object file built for OSX, for architecture ..."

Recently I encountered XCode 7 link error when compiling iOS simulator.  The error was "Building for iOS simulator, but linking in object file built for OSX, for architecture i386". After adding "-O2 -m32 -miphoneos-version-min=5.0" to the compiler switch, the problem went away.