Use zeroinitializer for (trailing zero portion of) large array initializers
more reliably.

This re-commits r333044 with a fix for PR37560.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@333141 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed