Have you seen this note (from https://cran.r-project.org/bin/macosx/)?
Important: this release uses Clang 7.0.0 and GNU Fortran 6.1, neither of
which is supplied by Apple. If you wish to compile R packages from sources,
you will need to download and install those tools - see the tools
directory.
Hi Spencer,
I remember having a similar error a few years ago when trying to compile R (and
its recommended packages, e.g. mgcv) from source. I was using clang as a
compiler (this is what Hadley recommends in his book "R packages"), and I
solved the issue by going back to g++. This can be done
