[lsan] Introduce print_suppressions flag.

Introduce a flag to either always or never print matched suppressions.
Previously, matched suppressions were printed unconditionally if there were
unsuppressed leaks. Also, verbosity=1 no longer has the semantics of "always
print suppressions and summary".

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@197510 91177308-0d34-0410-b5e6-96231b3b80d8