Note that it is ok with the raw mpich patch 
guix time-machine --commit=398ec3c1e265a3f89ed07987f33b264db82e4080 -- time-machine --url=https://gitlab.inria.fr/bremond/guix.git --branch=add-mpich -- build mumps-openmpi --with-input=openmpi=mpich    

I tried a build with the same hwloc as the embedded commit f7b08df258c2e7d04ca2035ddd55a1de91f806d4
(the HEAD used for hwloc in mpich) but the result is the same:

guix time-machine --commit=398ec3c1e265a3f89ed07987f33b264db82e4080 -- time-machine --url=https://gitlab.inria.fr/bremond/guix.git --branch=test-mpich -- build mumps-openmpi --with-input=openmpi=mpich

(the 2 steps time-machine needed is another question...)


Maurice