Make the big array in the UBSan C++ runtime be zero-initialized to dramatically
shrink the binary size of the ubsan runtime.

Also fix a bug where long-running processes could eventually trigger a crash in
the runtime by filling up the cache. I've not found a nice way to add a test for
this crasher; ideas welcome.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@192931 91177308-0d34-0410-b5e6-96231b3b80d8