[Openmp-dev] More cmake breakage

[C Bergström via Openmp-dev]

Are you doing something in your cmake that would cause these to be
ignored if manually set? If so please don't.

    CMAKE_ASM_COMPILER
    arch
---------------
Please don't assume that the config header (omp_lib.h) will be written
to the source dir/. This is a bad/wrong assumption and breaking our
nightly builds.


-- Build files have been written to:
/bamboo-agent-home/xml-data/build-dir/DEBUG/build/openmp-llvm/build-x86_64
[100%] Built target openmp-cmake-x86_64
Scanning dependencies of target openmp-make-x86_64
gmake[3]: warning: jobserver unavailable: using -j1.  Add `+' to
parent make rule.
Scanning dependencies of target libomp-mod
gmake[5]: *** No rule to make target
`/bamboo-agent-home/xml-data/build-dir/DEBUG/src/openmp-llvm/runtime/src/omp_lib.h',
needed by `src/omp_lib.mod'.  Stop.
gmake[4]: *** [src/CMakeFiles/libomp-mod.dir/all] Error 2
gmake[3]: *** [all] Error 2
-------------
These changes really need to be posted in advance for review. If I
missed them I apologize. (Was this part of the review for removing
makefiles?)