Fix maphys ctest to allow tests with more MPI processes than cores

Allow tests with more MPI processes than available CPU cores during the ctest
process, which otherwise is not allowed by default by OpenMPI.

inria/hiepacs.scm

@@ -105,7 +105,14 @@ area (CPUs-GPUs, distributed nodes).")
      '(#:configure-flags '("-DMAPHYS_BUILD_TESTS=ON"
                            "-DMAPHYS_SDS_MUMPS=ON"
                            "-DMAPHYS_SDS_PASTIX=ON")
-                         ))
+
+       #:phases (modify-phases %standard-phases
+                   (add-before 'check 'prepare-test-environment
+                   (lambda _
+                     ;; Allow tests with more MPI processes than available CPU cores,
+                     ;; which is not allowed by default by OpenMPI
+                     (setenv "OMPI_MCA_rmaps_base_oversubscribe" "1"))))))
+
     (inputs `(("hwloc" ,hwloc "lib")
               ("openmpi" ,openmpi)
               ("ssh" ,openssh)