[patch][m68k] Remove sched_branch_type, reduce genattrtab run time to reasonable numbers

[Steven Bosscher <stevenb dot gcc at gmail dot com>]

Hello,

Since around trunk r135033, m68k has some scheduler attributes that
are computed by C functions in m68k.c. Together with Richard
Sandiford's improvements to genattrtab optimizations, the run time for
genattrtab for m68k is >9 minutes on a fast machine (gcc110).

With the attached patch, genattrtab goes down to less than 2 minutes.

But the only thing the patch does, is remove a write-only array,
sched_branch_type! This array was apparently introduced to compute the
best type-attribute for four branch instructions, with a FIXME that
someone should implement the actual computations for the best type.
However, exactly four years have passed since this code was added, and
nobody has bothered to actually implement this better type attribute
assignment.To me, it makes no sense to keep this code around, given
the problems it creates for genattrtab.

Tested by building a cross to m68k-linux. OK for trunk?

Ciao!
Steven

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