Thanks Stephen and Florian for your input. It's now clear that a package
that only adds the "missing pieces" won't work.
Stephen John Smoogen wrote:
1. Make a non-default module which contained all the rebuilt
binaries
needed to make gcc-gnat and other tools work (some languages also need
other utilities rebuilt to work).
2. Make an SCL which contains all these.
3. Make a set of rpms which installed gcc<name> in all the same places
as gcc but didn't collide
The module option seems like it would be easiest to use for the users,
and would also avoid the risk that one program might invoke the wrong
build of another program.
Björn Persson