[UBSan] Initialize symbolizer inside __ubsan::Init().

We used to initialize symbolizer lazily, but this doesn't work in
various sandboxed environments. Instead, let's be consistent with
the rest of sanitizers.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@214006 91177308-0d34-0410-b5e6-96231b3b80d8