Macports keeps 3 different versions of LLVM installed I am using the latest Macports 2.3.3 on OS X 10.10.3. I installed Gimp, Ufraw and Enblend (among others), which required py27-numpy, which gave me 2 different versions of LLVM: 

$ port rdependents llvm-3.3
The following ports are dependent on llvm-3.3:
  ld64-latest
    ld64
      clang-3.5
      libgcc
        py27-numpy
          py27-pygtk
            gimp2
              gimp-app
                gimp
              gimp-jp2
              gimp-lqr-plugin
              gutenprint
              icns-gimp
              ufraw
              xsane
          vigra
            enblend

$ port rdependents llvm-3.4
The following ports are dependent on llvm-3.4:
  cctools
    libgcc
      py27-numpy
        py27-pygtk
          gimp2
            gimp-app
              gimp
            gimp-jp2
            gimp-lqr-plugin
            gutenprint
            icns-gimp
            ufraw
            xsane
        vigra
          enblend


For some reason, I even have llvm-3.5:

$ port rdependents llvm-3.5
The following ports are dependent on llvm-3.5:
  clang-3.5
$ port rdependents clang-3.5
clang-3.5 has no dependents.


This means that upgrading Macports builds LLVM 3 times in various versions, which takes a ton of time and heats up the Earth and whatnot :)

Is there any way to streamline this? Somehow tell the packages "go use llvm-3.5"?
I was forced to uninstall all packages depending on llvm-3.3 and llvm-3.4, and then reinstall them. In my case, all of reinstalled packages had dependencies on llvm-3.5, not on llvm-3.3/3.4, thus there were no problems when I uninstalled both llvm-3.3 and llvm-3.4. I hope it works for you.