IR: Stop copying vectors of TrackingMDRef in DIBuilder

No real functionality change here, just avoiding an unnecessary copy of
std::vector<TrackingMDRef> for every subprogram with variables.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@266907 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed