I got the following error when I was trying to installing Julia brew install --64bit julia:
Error: julia dependency fftw was built with the following
C++ standard library: libstdc++ (from clang)
This is incompatible with the standard library being used
to build julia: libc++ (from clang)
As I understood, the problem was that fftw was already installed without the --with-fortran option.
Reinstalling fftw with --with-fortran option solved the problem.
brew reinstall --with-fortran fftw
Hope this will save somebody's time.