Xcode 10 (iOS 12) does not contain libstdc++6.0.9

libstdc++ was deprecated 5 years ago. Apple's more recent platforms (tvOS and watchOS) don't support it.

Support was removed from the iOS 12.0 Simulator runtime, but it remains in the iOS 12.0 (device) runtime for binary compatibility with shipping apps.

You should update your project to use libc++ rather than libstdc++ by setting the CLANG_CXX_LIBRARY build setting ("C++ Standard Library") to libc++.

If you have any static libraries that depend on libstdc++.tbd, you can workaround it for now by copying the file from the SDKs in Xcode 9.4 (and libstdc++.*.dylib in the iOS simulator runtime), but that is not a long term solution. You should contact the provider of those libraries and request versions built using libc++.

You may copy it from old Xcode(9.4). It should work.

cp /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/lib/libstdc++.* /Applications/Xcode-beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/lib/cp /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk/usr/lib/libstdc++.* /Applications/Xcode-beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk/usr/lib/

libstdc++ is removed in iOS 12.

I wish I had a better source than an Apple engineer on Twitter, but that's all I have.

@jeremyhuPSA: libstdc++ is gone from the iOS 12.0 SDK (it is present in the runtime for binary compatibility). It's days are numbered on macOS as well. Migrate over to libc++ if you haven't already. #WWDC2018 #cplusplus

Edit: Here's a better source, Xcode 10 patch notes

Building with libstdc++ was deprecated with Xcode 8 and is not supported in Xcode 10 when targeting iOS. C++ projects must now migrate to libc++ and are recommended to set a deployment target of iOS 7 or later. Besides changing the C++ Standard Library build setting, developers should audit hard-coded linker flags and target dependencies to remove references to libstdc++ (including -lstdc++, -lstdc++.6.0.9, libstdc++.6.0.9.tbd, and libstdc++.6.0.9.dylib). Project dependencies such as static archives that were built against libstdc++ will also need to be rebuilt against libc++. (40885260)