title: Missing "libsystem_darwin.dylib" after installing Xcode 9
body: <p>I want to install <a href="https://bioconductor.org/packages/release/bioc/html/GenomicAlignments.html" rel="noreferrer">GenomicAlignments</a> R package, however the installation crushes because it can't install one of the dependancies which is <code>RCurl</code>. When I try to install <code>RCurl</code> alone by running <code>install.packages("RCurl")</code>, I get the following error:</p>
  
  <pre><code>ld: file not found: /usr/lib/system/libsystem_darwin.dylib for architecture x86_64
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  make: *** [RCurl.so] Error 1
  ERROR: compilation failed for package ‘RCurl’
  * removing ‘/usr/local/lib/R/3.4/site-library/RCurl’
  Warning in install.packages :
    installation of package ‘RCurl’ had non-zero exit status
  </code></pre>
  
  <p>This is the <code>sessionInfo()</code>:</p>
  
  <pre><code>R version 3.4.2 (2017-09-28)
  Platform: x86_64-apple-darwin16.7.0 (64-bit)
  Running under: macOS Sierra 10.12.6
  </code></pre>
  
  <p>I <a href="https://forums.developer.apple.com/thread/87829" rel="noreferrer">traced it down</a> to faulty Xcode 9 version which I installed recently. So, any ideas on how to fix this? Going back to Xcode 8.3.3 would probably fix the problem, but I have no idea how to do this.</p>
  
  <p>Thanks in advance,
  TP</p>