Don't allocate the DIBuilder on the heap and remove all the complexity
that ensued from that.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186777 91177308-0d34-0410-b5e6-96231b3b80d8
Don't crash when llvm.compiler.used becomes empty.

GlobalOpt simplifies llvm.compiler.used by removing any members that are also
in the more strict llvm.used. Handle the special case where llvm.compiler.used
becomes empty.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186778 91177308-0d34-0410-b5e6-96231b3b80d8