title: R keeps asking about "installing from sources that need compilation"
body: <p>I am trying to install packages (<code>devtools</code>, <code>plyr</code> and several others) and keep getting stuck with the same problem, which seems to appear for some packages more often than others</p>
  
  <pre><code> There are binary versions available but the
    source versions are later:
            binary source needs_compilation
  processx  2.0.0.1  3.2.1              TRUE
  desc        1.1.1  1.2.0             FALSE
  callr       1.0.0  3.1.1             FALSE
  git2r      0.21.0 0.24.0              TRUE
  rcmdcheck   1.2.1  1.3.2             FALSE
  usethis     1.1.0  1.4.0             FALSE
  devtools   1.13.4  2.0.1             FALSE
  
  Do you want to install from sources the packages which need compilation?
  </code></pre>
  
  <p>OK, well, I honestly have no idea what that means, but chances are 50/50</p>
  
  <p>Whether I choose y or n I end up with:</p>
  
  <pre><code>Packages which are only available in source
    form, and may need compilation of
    C/C++/Fortran: ‘ps’ ‘fs’ ‘pkgload’
  Do you want to attempt to install these from sources?
  y/n: 
  </code></pre>
  
  <p>and whether I choose y or n here I end up with</p>
  
  <pre><code>Warning in install.packages :
    installation of package ‘devtools’ had non-zero exit status
  
  The downloaded source packages are in
  ‘/private/var/folders/zz/mxrvmdvd2j399kfylbspjp4r0000gn/T/Rtmp1OdcyF/downloaded_packages’
  </code></pre>
  
  <p>I am operating on Mac Mojave 10.4.2 
  with RStudio 1.1.463</p>
  
  <p>My expected result was for the package to be installed and I could use something like
      library(package) 
  to get started with my work.</p>
  
  <p>I am somewhat experienced in working with R and have never encountered this problem until recently? Do I need to update sth? Change a setting?</p>
  
  <p>UPDATE: <code>ggplot2</code> and <code>biomod2</code> are showing the same issue
  UPDATE: seems to be no problem with R (not RStudio) and the R package manager.... why is this the case?</p>