Update package requirements documentation

docs/spack-package_requirements.org

@@ -10,10 +10,12 @@ the other packages are compiled
   - Octoups~OpenMP requires ELPA~OpenMP (pkconfig unconditionally brings in ~-fopenmp~ -> Octopus would compile with OpenMP; hence we cannot support it)
 - In EasyBuild ELPA is provided with and without OpenMP support in one prefix
   (different sonames)
-- In Spack up to release ~23c~ we only provide ELPA with OpenMP support
-- [TODO: FINAL DECISION REQUIRED] In Spack starting from release ~24a~ we
-  replicate EasyBuild and provide ELPA with and without OpenMP support under the
-  same prefix
+- From MPSD software release ~24b~ onwards we provide both versions separately. We change the module name to elpa-openmp for elpa+openmp to avoid
+  the name clash. Both modules are loaded via the octopus-dependencies/full metamodule. We rely on the Octopus CMake configuration to pick up
+  the desired one.
+- In MPSD software release ~24a~ we replicate EasyBuild and provide ELPA with
+  and without OpenMP support under the same prefix
+- In MPSD software release ~23c~ we only provide ELPA with OpenMP support
 - In a GPU toolchain ELPA may need CUDA support
 
 ** DFTB+
@@ -65,15 +67,12 @@ the other packages are compiled
 - the intel compiler does not bring its own C++ standard library; instead it uses
   gcc to get the standard library; hence the stdlibrary version depends on the
   gcc version visible to the intel compiler
-- we can use additional flags to help pick the correct gcc
-  (https://spack.readthedocs.io/en/latest/build_systems/intelpackage.html#installing-intel-tools-within-spack)
-  #+begin_quote
-  Use the modules: and/or cflags: tokens to further specify a suitable
-  accompanying gcc version to help pacify picky client packages that ask for C++
-  standards more recent than supported by your system-provided gcc and its
-  libstdc++.so.
-  #+end_quote
-  *NOTE* the docs say **more recent that ... system**, which might indicate why we still see some problems
+- by installing intel-oneapi-compilers[-classic]%gcc@toolchain Spack
+  automatically configures the intel compiler (bin/icx.cfg and similar) in a way
+  that it depends on the correct gcc. Passing ~-gcc/gxx-name~ or
+  ~-gcc-toolchain~ explicitly is not required. (We did this in the 24a release
+  because we did not know about the configuration files; adding these flags has
+  been removed from mpsd-software in Dec. 2024)
 ** GCC compatibility
 - intel classic (~icc~ and ~icpc~) not compatible with gcc>12 (the compiler has been discontinued, so this is unlikely to ever change)
  - This has been [[https://gitlab.gwdg.de/mpsd-cs/spack-environments/-/merge_requests/109#note_1181314][verified by Jehferson Mello]] (observed issue: incompatibility with C++ std library headers)
@@ -152,7 +151,7 @@ the other packages are compiled
 - anaconda3 cannot be used as of 2024 due to license restrictions (MPSD would need to pay for a commercial license)
 - we instead provide miniforge3
 - we restrict it to the ~conda-forge~ channel (in a ~.condarc~ in the miniforge3 directory)
-  (the more flexible ~denylist_channels~ introduced in conda 24.9 seems to have a bug)
+  (the more flexible ~denylist_channels~ introduced in conda 24.9 have a bug)
 - users are advised to use the conda module when they want to create their own conda environments
   (that way we can ensure no one uses the commercial channels on the HPC system)
 - we provide a custom environment, currently called ~python-3.12~ with commonly used packages preinstalled

[Hans Fangohr]

Good documentation - thank you.