title: clang-7: error: linker command failed with exit code 1 for macOS Big Sur
body: <p>Installing R packages that need compiling in macOS is broken since Big Sur.  Here is such an example.</p>
  <pre><code>&gt; install.packages('nlme')
  
    There is a binary version available but the source version is later:
        binary  source needs_compilation
  nlme 3.1-150 3.1-151              TRUE
  
  Do you want to install from sources the package which needs compilation? (Yes/no/cancel) Yes
  installing the source package ‘nlme’
  
  trying URL 'https://cran.rstudio.com/src/contrib/nlme_3.1-151.tar.gz'
  Content type 'application/x-gzip' length 805592 bytes (786 KB)
  ==================================================
  downloaded 786 KB
  
  * installing *source* package ‘nlme’ ...
  ** package ‘nlme’ successfully unpacked and MD5 sums checked
  ** using staged installation
  ** libs
  &quot;gfortran-4.8&quot; -fno-optimize-sibling-calls  -fPIC  -Wall -g -O2  -c chol.f -o chol.o
  gfortran-4.8: warning: couldn’t understand kern.osversion ‘20.1.0
  clang -mmacosx-version-min=10.13 -I&quot;/Library/Frameworks/R.framework/Resources/include&quot; -DNDEBUG   -I/usr/local/include   -fPIC  -Wall -g -O2  -c corStruct.c -o corStruct.o
  clang -mmacosx-version-min=10.13 -I&quot;/Library/Frameworks/R.framework/Resources/include&quot; -DNDEBUG   -I/usr/local/include   -fPIC  -Wall -g -O2  -c gnls.c -o gnls.o
  clang -mmacosx-version-min=10.13 -I&quot;/Library/Frameworks/R.framework/Resources/include&quot; -DNDEBUG   -I/usr/local/include   -fPIC  -Wall -g -O2  -c init.c -o init.o
  clang -mmacosx-version-min=10.13 -I&quot;/Library/Frameworks/R.framework/Resources/include&quot; -DNDEBUG   -I/usr/local/include   -fPIC  -Wall -g -O2  -c matrix.c -o matrix.o
  clang -mmacosx-version-min=10.13 -I&quot;/Library/Frameworks/R.framework/Resources/include&quot; -DNDEBUG   -I/usr/local/include   -fPIC  -Wall -g -O2  -c nlOptimizer.c -o nlOptimizer.o
  clang -mmacosx-version-min=10.13 -I&quot;/Library/Frameworks/R.framework/Resources/include&quot; -DNDEBUG   -I/usr/local/include   -fPIC  -Wall -g -O2  -c nlme.c -o nlme.o
  clang -mmacosx-version-min=10.13 -I&quot;/Library/Frameworks/R.framework/Resources/include&quot; -DNDEBUG   -I/usr/local/include   -fPIC  -Wall -g -O2  -c nlmefit.c -o nlmefit.o
  clang -mmacosx-version-min=10.13 -I&quot;/Library/Frameworks/R.framework/Resources/include&quot; -DNDEBUG   -I/usr/local/include   -fPIC  -Wall -g -O2  -c pdMat.c -o pdMat.o
  clang -mmacosx-version-min=10.13 -I&quot;/Library/Frameworks/R.framework/Resources/include&quot; -DNDEBUG   -I/usr/local/include   -fPIC  -Wall -g -O2  -c pythag.c -o pythag.o
  &quot;gfortran-4.8&quot; -fno-optimize-sibling-calls  -fPIC  -Wall -g -O2  -c rs.f -o rs.o
  gfortran-4.8: warning: couldn’t understand kern.osversion ‘20.1.0
  clang -mmacosx-version-min=10.13 -dynamiclib -Wl,-headerpad_max_install_names -undefined dynamic_lookup -single_module -multiply_defined suppress -L/Library/Frameworks/R.framework/Resources/lib -L/usr/local/lib -o nlme.so chol.o corStruct.o gnls.o init.o matrix.o nlOptimizer.o nlme.o nlmefit.o pdMat.o pythag.o rs.o  -F/Library/Frameworks/R.framework/.. -framework R -Wl,-framework -Wl,CoreFoundation
  ld: framework not found CoreFoundation
  clang-7: error: linker command failed with exit code 1 (use -v to see invocation)
  make: *** [nlme.so] Error 1
  ERROR: compilation failed for package ‘nlme’
  * removing ‘/Library/Frameworks/R.framework/Versions/4.0/Resources/library/nlme’
  * restoring previous ‘/Library/Frameworks/R.framework/Versions/4.0/Resources/library/nlme’
  Warning in install.packages :
    installation of package ‘nlme’ had non-zero exit status
  
  The downloaded source packages are in
      ‘/private/var/folders/_3/b8whcf8d1bb8w_lr2rrscb5m0000gp/T/RtmpWCjwfs/downloaded_packages’
  
  </code></pre>
  <p>I've tried reinstalling xcode and Command Line Tools and completed Brew update + upgrade.  Any suggestions appreciated.</p>