Hi Guys,
FYI: I have already opened a pull request to enhance redhat-rpm-config to allow packages to build with clang instead of gcc if they so wish:
https://src.fedoraproject.org/rpms/redhat-rpm-config/pull-request/82
The patch makes use of clang's CCC_OVERIDE_OPTIONS to process the options that are normally passed to gcc as well loading clang specific options from a configuration file. The patch also creates variables called __cc, __cxx and __cpp which are initialised as might be expected, but which a package could override to point to some other compiler should it wish to do so.
Cheers Nick