[PGO] Handle cases of non-instrument BBs

As shown in PR41279, some basic blocks (such as catchswitch) cannot be
instrumented. This patch filters out these BBs in PGO instrumentation.
It also sets the profile count to the fail-to-instrument edge, so that we
can propagate the counts in the CFG.

Differential Revision: https://reviews.llvm.org/D62700

llvm-svn: 362995