Callgrind: make globals for log_* helpers visible outside sim.c

Callgrind: make globals for log_* helpers visible outside sim.c

At beginning of each BB, Callgrind inserts a call to setup_bbcc,
which (among a lot other things), sets global vars needed for
the log_* helpers called afterwards in this BB.

These globals, bb_base and cost_base, previously we static declared
and only visible in sim.c. Make them visible also in the rest of
callgrind to allow for log_* handlers outside sim.c.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@11166