Changes for aarch64

Hi @kolos, can you merge these changes for the aarch64 architecture ?

It defines a new config/ file for aarch64-centos7, and makes two minor adjustments in the CMakeLists.txt file"

Use of ZLIB for ziop (which implies using FindZLIB.cmake) is required in cross-compilation mode, or we pick up the zlib version from the host.

The omnicpp executable should have no dependencies on omniidlmodule or python, it's just a C preprocessor (?)

cheers, Reiner