Add option to override CMake's ConfigVersion.cmake.in template.
Add option to override CMake's ConfigVersion.cmake.in template.

CMake's write_basic_package_version_file() function uses a set of
files BasicConfigVersion-....cmake.in to configure the package
ConfigVersion.cmake file. These templates contain code that
compare the pointer word size between the calling find_package()
environment and that used when the package was built, in a
misguided attempt to enforce ABI compatibility.

For packages that just supply executables, this test is
simply counter-productive, particularly in a cross-compilation
environment.

This patch allows one to use one's own ConfigVersion template
file.

jafyvilla/CMake,ptoharia/CMake,biddisco/CMake,ptoharia/CMake,jafyvilla/CMake,ptoharia/CMake,biddisco/CMake,shurikasa/CMake,shurikasa/CMake,jafyvilla/CMake,shurikasa/CMake,biddisco/CMake,shurikasa/CMake,jafyvilla/CMake,biddisco/CMake,ptoharia/CMake