Default ISA/tuning flags for GCC, --enable-kernel= level for glibc

[Bill Nottingham]

Jakub Jelinek (jakub at redhat.com) said: 
> > I agree.  Does it have to be .29, or would something slightly older (and
> > theoretically more stable) suffice?  The .27.x release has been in use for
> > F-9 and F-10 for a while now.
> 
> For glibc 2.9 (F10) it would suffice to just have .27, but for rawhide
> .29 introduces futex bitset and realtime clock support, which means an extra
> syscall for every threaded program.  We could bump it in steps, first start
> requiring .27 and then if .29 is sufficiently stable in a month (or when
> we really need to freeze), rebuild just glibc requiring a newer kernel.

Realistically, the build environment we support both for ourselves
to build on, and what we tell our customers and users to use, is mock.
Mock relies on the host kernel version. Heck, call it the build hypervisor.

Moreover, you still have to support the oldest kernel you want to support
a live upgrade from, otherwise your system will fall over partway through
the transaction.

Hence, for Fedora 11, I don't see how we can set the required kernel
to anything greater than 'the RHEL 5 version'. Whether that's 2.6.18 directly,
or some later version that encapsulates both 2.6.18 and whatever backports
were made to the RHEL 5 kernel, should be determined.

Bill