IR: Move MDStrings to a BumpPtrAllocator

We never delete any MDString until the context is destroyed.  Might as
well throw them onto a BumpPtrAllocator.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@265520 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed