[R-SIG-Mac] How to get a Fortran compiler compatible to Xcode?

[Marius Hofert]

Hi,

I'm running Mac OS X Yosemite 10.10.3 on a MacBook Pro (Retina,
13", 2015). I would like to install R from source (various
versions etc.) and thus installed Xcode (latest version:
6.3.1). How can I get a Fortran compiler which is compatible with Xcode 6.3.1?

Here is what I tried:
1) I used to download and install gfortran-lion-5666-3.pkg from
http://r.research.att.com/tools but I now obtain "... can't be
installed on this disk. This package requires Xcode 4.1 with
gcc-4.2 (build 5666.3)". It seems that my (newer) Xcode version
is not recognized.
2) I then installed gfortran-4.2.3.dmg from CRAN -> Download R
for (Mac) OS X -> tools. This worked fine, but then I ran into this issue:
I wanted to install MPI and thus downloaded and unpacked
openmpi-1.8.5.tar.gz from http://www.open-mpi.org/software/ompi/
but ./configure leads to an error:

...
checking if C and Fortran are link compatible... no
**********************************************************************
It appears that your Fortran compiler is unable to link against
object files created by your C compiler.  This typically indicates
one of a few possibilities:

  - A conflict between CFLAGS and FCFLAGS
  - A problem with your compiler installation(s)
  - Different default build options between compilers (e.g., C
    building for 32 bit and Fortran building for 64 bit)
  - Incompatible compilers

Such problems can usually be solved by picking compatible compilers
and/or CFLAGS and FCFLAGS.  More information (including exactly what
command was given to the compilers and what error resulted when the
commands were executed) is available in the config.log file in this
directory.
**********************************************************************
configure: error: C and Fortran compilers are not link compatible.
Can not continue.
sklar-2:openmpi-1.8.5 mhofert$

I found this post
(http://grokbase.com/t/r/r-sig-mac/14awnd0341/compiling-r-3-1-1-sources-under-os-x-yosemite)
which seems to be related, but since there are no clear
instructions/scripts given, I still don't have a solution.

How can I get a suitable/compatible Fortran compiler?

Thanks & cheers,
Marius