Document multi-configuration build support in CMake

doc/src/Build_cmake.rst

@@ -150,6 +150,42 @@ for IDEs like Eclipse, CodeBlocks, or Kate can be selected using the *-G*
 command line flag.  A list of available generator settings for your
 specific CMake version is given when running ``cmake --help``.
 
+.. _cmake_multiconfig:
+
+Multi-configuration build systems
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Throughout this manual it is mostly assumed that LAMMPS is being built
+on a Unix-like operating system with "make" as the underlying "builder",
+since this is the most common case.  In this case the build "configuration"
+is chose using ``-D CMAKE_BUILD_TYPE=<configuration>`` with ``<configuration>``
+being one of "Release", "Debug", "RelWithDebInfo", or "MinSizeRel".
+Some build tools, however, can also use or even require to have a so-called
+multi-configuration build system setup.  For those the built type (or
+configuration) is chosen at compile time using the same build files. E.g.
+with:
+
+.. code-block:: bash
+
+   cmake --build build-multi --config Release
+
+In that case the resulting binaries are not in the build folder directly
+but in sub-directories corresponding to the build type (i.e. Release in
+the example from above).  Similarly, for running unit tests the
+configuration is selected with the *-C* flag:
+
+.. code-block:: bash
+
+   ctest -C Debug
+
+The CMake scripts in LAMMPS have basic support for being compiled using a
+multi-config build system, but not all of it has been ported.  This is in
+particular applicable to compiling packages that require additional libraries
+that would be downloaded and compiled by CMake.  The "windows" preset file
+tries to keep track of which packages can be compiled natively with the
+MSVC compilers out-of-the box.  Not all of those external libraries are
+portable to Windows either.
+
 
 Installing CMake
 ^^^^^^^^^^^^^^^^

doc/src/Build_windows.rst

@@ -89,6 +89,11 @@ miss the correct master ``CMakeLists.txt``.  Try to open the
 starting point.  It is also possible to configure and compile LAMMPS
 from the command line with a CMake binary from `cmake.org <https://cmake.org>`_.
 
+Please note, that for either approach CMake will create a so-called
+:ref:`"multi-configuration" build environment <cmake_multiconfig>`, and
+the command lines for building and testing LAMMPS must be adjusted
+accordingly.
+
 To support running in parallel you can compile with OpenMP enabled using
 the OPENMP package or install Microsoft MPI (including the SDK) and compile
 LAMMPS with MPI enabled.