CLion won't compile existing project once Mac upgraded to XCode 9.

I have a project that compiled under CLion before the Mac upgraded to XCode 9.  I have installed the command line and accepted the software agreement.

CLion complains:

clang: warning: no such sysroot directory: '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk' [-Wmissing-sysroot]

And it is correct, that sdk is not there.  Just MacOSX.sdk and MacOSX10.13.sdk, an alias.

Thanks

Tim