[llvm] Fix compiler errors in GVN.h for clang versions older than 15 (PR #107636)

[Michael Jones via llvm-commits]

michaelrj-google wrote:

Please either revert the original commit or land this commit to fix the issue. The libc runtimes builder is currently broken on this issue since it is on clang 14: https://lab.llvm.org/buildbot/#/builders/78/builds/5463



https://github.com/llvm/llvm-project/pull/107636