[petsc-users] Cannot find a C preprocessor OSX

[Denis Davydov]

> On 19 Mar 2016, at 20:00, Satish Balay <balay at mcs.anl.gov> wrote:
> 
> But I would think 'mpicc -show' should show this. [if spack is setting
> up these options via MPI wrappers]

they set up compiler wrappers (clang in this case), where they pass -L and -I flags for all 
libraries used to build a package 
http://software.llnl.gov/spack/packaging_guide.html#compiler-interceptors
And then compiled OpenMPI is set to use those wrappers.

That’s why there are those unused flags. 
I would try to add -Qunused-arguments to their wrappers in case of clang compiler so that 
clang does not complain about unused flags in any package.

Regards,
Denis.