[libsanitizer] Unmapping the old cache partially invalidates the memory layout, so add
a flag to skip cache update for cases when that's unacceptable (e.g. lsan).

Patch by Sergey Matveev (earthdok@google.com)



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@178000 91177308-0d34-0410-b5e6-96231b3b80d8