Fix nodiscard for volatile references

As reported here https://bugs.llvm.org/show_bug.cgi?id=34988
[[nodiscard]] warnings were not being suppressed for
volatile-ref return values.

Differential Revision: https://reviews.llvm.org/D39075


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@316166 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed