document custom linker choice

     of mis-compiled code (or an undesired large loss of precision due

     to significant reordering of operations and thus less error cancellation).

Use custom linker for faster link times when ENABLE_TESTING is active

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

When compiling LAMMPS with enabled tests, most test executables will

need to be linked against the LAMMPS library.  Since this can be a

large with many C++ objects when many packages are enabled, link times

can become very long on machines that use the GNU BFD linker (e.g.

Linux systems).  Alternatives like the ``lld`` linker of the LLVM project

or the ``gold`` linker available with GNU binutils can speed up this step

substantially. CMake will by default test if any of the two can be

enabled and use it when ``ENABLE_TESTING`` is active.  It can also be

selected manually through the ``CMAKE_CUSTOM_LINKER`` CMake variable.

Allowed values are ``lld``, ``gold``, ``bfd``, or ``default``.  The

``default`` option will use the system default linker otherwise, the

linker is chosen explicitly.  This option is only available for the

GNU or Clang C++ compiler.

Tests for other components and utility functions

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

bilayers

binsize

binstyle

binutils

biomolecular

biomolecule

Biomolecules