Improve profile quality reporting by 1) fixing a format issue for small
binaries, 2) adding new stats for exception handling usage, 3) excluding
selected blocks when computing the CFG flow conservation score.
More specifically for 3), we are excluding blocks that satisfy at least
one of the following characteristics: a) is a landing pad, b) has at
least one landing pad with non-zero execution counts, c) ends with a
recursive call. The reason for a) and b) is because the thrower -->
landing pad edges are not explicitly represented in the CFG. The reason
for c) is because the call-continuation fallthrough edge count is not
important in case of recursive calls.
Modified test `bolt/test/X86/profile-quality-reporting.test`.
Added test `bolt/test/X86/profile-quality-reporting-small-binary.s`.
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