Xcode 10.2 GNU-style inline assembly is disabled

In your WatchKit Extension target (or whatever target it's complaining this for), add -fgnu-inline-asm to the Other C Flags build options. You'll need to file a radar as well as it looks like a bug.

Remove your custom the Enable Bitcode build setting (ENABLE_BITCODE) on WatchKit Extension target can solve the problem.

All watchOS and tvOS force to enable Bitcode, your custom build settings will cause error from Xcode 10.2 (ignored before Xcode 10.1). on iOS this is optional, and macOS is not supported.

This is often a mistake that you set this value in xcconfig or Project-Level build settings. The correct way for setting Bitcode on iOS target, is to only change the build setting on Tarfet-Level (or wrriting xcconfig with SDK filter)