Dear John,
I can see you have specified everything the standard autoconf way, but unfortunately Molpro's blas/lapack detection does not play so well with that yet. This is mainly just historical, and where possible we've moved to the standard variables, but I don't think we're quite ready yet with blas/lapack so you will need to use the --with-lapack options.
I note you are using '../configure', Molpro doesn't support an out of source build so it will really need to be './configure' in the source tree. Also, if you have a GA install all that you need to do is ensure the resulting bin directory (containing ga-config) is in PATH and configure will use that to do the rest.
Here are some options to try:
1. Let configure try and find MKL automatically, hopefully will work based on MKLROOT being set:
./configure --prefix=/soft/molpro/2021.2 CPPFLAGS=-I/home/jlow/eigen/eigen-3.3.9 CFLAGS=-march=native CXXFLAGS=-march=native FCFLAGS=-march=native FC=mpif90
2. If that fails guide configure to the MKL lib directory by adding:
--with-lapack-path=$MKLROOT/lib/intel64
3. If you want to specify the libraries by hand instead use:
--with-lapack="-L$MKLROOT/lib/intel64 -lmkl_scalapack_lp64 -Wl,--no-as-needed -lmkl_gf_lp64 -lmkl_gnu_thread -lmkl_core -lmkl_blacs_intelmpi_lp64 -lgomp -lpthread -lm -ldl"
Hopefully the above or something similar should enable you to configure Molpro against MKL.
Best wishes,
Andy