Allow openmpi tests on systems with less than 4 processors

The MPI tests use up to four processes.  By default, OpenMPI won't allow
more processes than processors and the tests will fail on a two
processor VM.  Using the --oversubscribe option will allow the tests to
run.

mpich doesn't have this limit by default and doesn't need or support
this option.

Signed-off-by: Trent Piepho <tpiepho@gmail.com>

fftw.spec

@@ -339,6 +339,9 @@ for mpi in %{mpi_list} ; do
         # Force linking the _mpi.so libraries with the mpi libs.  This works because
         # we get rid of all of the non-mpi components of these builds
         export CC=mpicc
+        if [ $mpi = "openmpi" ]; then
+            export MPIRUN="mpirun --oversubscribe"
+        fi
         %{configure} ${BASEFLAGS} ${prec_flags[iprec]} \
             --enable-mpi \
             --libdir=%{_libdir}/$mpi/lib \
@@ -525,6 +528,7 @@ done
 - Enable AVX2 on x86-86
 - Enable NEON on aarch64
 - Clean up precision list
+- Fix for OpenMPI build with < 4 processors
 
 * Thu Mar 02 2023 Orion Poplawski <orion@nwra.com> - 3.3.10-5
 - Use make macros