Merge branch 'develop' of https://github.com/jcsda/spack-stack into f…

…eature/update_derecho

doc/source/NewSiteConfigs.rst

@@ -143,6 +143,14 @@ These instructions are meant to be a reference that users can follow to set up t
    brew install qt@5
    brew install mysql
 
+.. note::
+  On an Intel based Mac, you will need to also install pkg-config using homebrew.
+  This is done to work around an issue where libraries (eg, openssl) cannot be properly found during code compilation.
+
+.. code-block:: console
+
+  brew install pkg-config  # Intel based Mac only
+
 4. Configure your terminal to use the homebrew installed bash
 
   After installing bash with homebrew, you need to change your terminal application's default command to use :code:`$HOMEBREW_ROOT/bin/bash`.
@@ -220,6 +228,14 @@ Remember to activate the ``lua`` module environment and have MacTeX in your sear
    # The texlive bin directory must have been added to PATH (see above)
    spack external find --scope system texlive
 
+.. note::
+  On an Intel based Mac, you need to add the following spack config command to prevent spack from building pkg-config.
+  This will force spack to use the pkg-config installed by homebrew (see above).
+
+.. code-block:: console
+
+  spack config --scope system add packages:pkg-config:buildable:false  # Intel based Mac only
+
 5. Find compilers, add to site config's ``compilers.yaml``
 
 .. code-block:: console