[CMake] cmake_c_compiler check

[bthomas at nexus.hu]

Hello,

I'm working on a code which uses openmpi and the goal would be to include its installation into the
cmakelists (easy-to-use reason).
I do it with a custom command which is fine but when i try to set CMAKE_C_COMPILER to the expected
executable cmake complains 
during the makefile generation that it cannot be found:

CMake Error: your C compiler: "/user/th/inst_release/bin/mpicc" was not found.   Please set
CMAKE_C_COMPILER to a valid compiler path or name.

This is due to the fact that in cmGlobalUnixMakefileGenerator3::EnableLanguage cmake checks for the
file, which is not yet there
during makefile generation of course. Do any of you got around this before? Or how can an official
solution be implemented?

Thanks to all:
Th