PETSc: Explicitly point to cpp when configuring

[eschnett]

I encountered an HPC system where PETSc's configure stage does not find a valid cpp (C preprocessor). Explicitly pointing to Spack's cpp wrapper resolves the problem.

[eschnett]

I do not understand these test failures. They seem unrelated to my changes?

[tgamblin]

@eschnett: develop was broken due to a couple earlier merges that didn't get along. I kicked off the build again and it's fixed.

[BarrySmith]

This "fix" is causing grief on both ANL Mira and OLCF systems. @sarich @balay

Sample bad output

# 3 "/tmp/petsc-RkoVhw/config.setCompilers/conftest.c" 2stderr:
/autofs/nccs-svm1_home1/mbt/spack/lib/spack/env/cpp: line 358: /autofs/nccs-svm1_home1/mbt/spack/bin/spack-cc-petsc@develop%gcc@5.3.0~boost~complex~debug+double+hdf5+hypre~int64+metis+mpi~mumps+shared+superlu-dist+trilinos arch=cray-CNL-interlagos /n4yqikl.in.log: No such file or directory
/autofs/nccs-svm1_home1/mbt/spack/lib/spack/env/cpp: line 359: /autofs/nccs-svm1_home1/mbt/spack/bin/spack-cc-petsc@develop%gcc@5.3.0~boost~complex~debug+double+hdf5+hypre~int64+metis+mpi~mumps+shared+superlu-dist+trilinos arch=cray-CNL-interlagos /n4yqikl.out.log: No such file or directory
Source:
#include "confdefs.h"
#include "conffix.h"
#include <stdlib.h>
Preprocess stderr before filtering:/autofs/nccs-svm1_home1/mbt/spack/lib/spack/env/cpp: line 358: /autofs/nccs-svm1_home1/mbt/spack/bin/spack-cc-petsc@develop%gcc@5.3.0~boost~complex~debug+double+hdf5+hypre~int64+metis+mpi~mumps+shared+superlu-dist+trilinos arch=cray-CNL-interlagos /n4yqikl.in.log: No such file or directory
/autofs/nccs-svm1_home1/mbt/spack/lib/spack/env/cpp: line 359: /autofs/nccs-svm1_home1/mbt/spack/bin/spack-cc-petsc@develop%gcc@5.3.0~boost~complex~debug+double+hdf5+hypre~int64+metis+mpi~mumps+shared+superlu-dist+trilinos arch=cray-CNL-interlagos /n4yqikl.out.log: No such file or directory
:
Preprocess stderr after filtering:/autofs/nccs-svm1_home1/mbt/spack/lib/spack/env/cpp: line 358: /autofs/nccs-svm1_home1/mbt/spack/bin/spack-cc-petsc@develop%gcc@5.3.0~boost~complex~debug+double+hdf5+hypre~int64+metis+mpi~mumps+shared+superlu-dist+trilinos arch=cray-CNL-interlagos /n4yqikl.in.log: No such file or directory/autofs/nccs-svm1_home1/mbt/spack/lib/spack/env/cpp: line 359: /autofs/nccs-svm1_home1/mbt/spack/bin/spack-cc-petsc@develop%gcc@5.3.0~boost~complex~debug+double+hdf5+hypre~int64+metis+mpi~mumps+shared+superlu-dist+trilinos arch=cray-CNL-interlagos /n4yqikl.out.log: No such file or directory:
              Popping language C

It seems that spack "cpp" is not the one that is needed. I would like to fix the problem by fixing PETSc to "find the correct CPP" but I need to know how it failed by looking at the failure in the PETSc configure.log file.

I am going to remove this code from the PETSc in the barry/xsdk branch and we'll experiment with finding a better fix.