cc/gcc: do not print 'core' or 'final'

In gcc-'s core and final passes, do not print 'core' or 'final' in
log messages. We already print it in step messages.

Also, as we use the core backend to build the bare-metal final gcc,
it can be disturbing to read 'core' while we're in fact in 'final'.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

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