DYLD_FALLBACK_LIBRARY_PATHにusr/lib/swiftの分も追加すれば、rpath指定無しでいける。

$ ROOT_PATH=$(xcrun --show-sdk-platform-path --sdk iphoneos)/Developer/Library/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot && \ DYLD_FALLBACK_FRAMEWORK_PATH=$ROOT_PATH/System/Library/Frameworks \ DYLD_FALLBACK_LIBRARY_PATH=$ROOT_PATH/usr/lib:$ROOT_PATH/usr/lib/swift \ DYLD_LIBRARY_PATH= \ DYLD_ROOT_PATH=$ROOT_PATH \ ./main

(edited)