Describe the enhancement requested

In #48414 we require support for C++20, but we didn't change any of R's configure, etc. scripts in that process to reference CXX20 instead of CXX17. This has generally been fine, though we are seeing what we suspect to be an issue with this in our Alpine build (in #48805).

Do we need to update this build infrastructure to be CXX20 instead of CXX17 like how we did this when we went from C++11 to C++17: 9d65981#diff-089697faebdb7820ca629a2bb316b878cc0ba18a5bfb0b60996f8dbcd1fa11e7L222-R221

Component(s)

C++, R