Fix bug 327238.

 assertion failure in Callgrind: bbcc.c:585 (vgCallgrind_setup_bbcc):
 Assertion 'passed <= last_bb->cjmp_count' failed

Background:
We want to detect the jump behavior of code, that is, the side exit
from a SB, as there can be many. For that, instrumented code writes
the exit number into a global variable (jmps_passed) before an eventual
exit.

With an exception happening in the first few instructions of an SB,
jmps_passed never was written, and still contained an old value. This
got saved/restored around the exception handler, and resulted in the
failed assertion.
Solution: always initialize jmps_passed to zero in setup_bbcc(), which
is called at the beginning of every SB.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13712 a5019735-40e9-0310-863c-91ae7b9d1cf9