[CMake] FindMPI.cmake in 3.11.4

[Burlen Loring]

Hi,

I'm trying to transition from cmake 3.8.2 to cmake 3.11.4. There are a 
number of changes the way FindMPI.cmake behaves in 3.11 that are making 
this difficult.

In 3.11 how do I override the settings? For instance I want to set 
MPI_C_LIBRARIES, MPI_C_INCLUDE_DIRS? In 3.8 all I had to do was set 
those variables myself, before find_package(MPI), and my setting were 
used. in 3.11 find_package(MPI) ignores, and wipes out my settings, and 
then fails.

Isn't it a defacto standard of cmake to be able to override find modules 
by setting the libraries and include dirs before the module runs?

Burlen