[Support] Make error banner optional in logAllUnhandledErrors

In a lot of places an empty string was passed as the ErrorBanner to
logAllUnhandledErrors. This patch makes that argument optional to
simplify the call sites.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346604 91177308-0d34-0410-b5e6-96231b3b80d8
25 files changed