
As decided on https://discourse.llvm.org/t/rfc-lets-document-and-enforce-a-minimum-python-version-for-lldb/82731. LLDB 20 recommended `>= 3.8` but did not remove support for anything earlier. Now we are in what will become LLDB 21, so I'm removing that support and making `>= 3.8` required. See https://docs.python.org/3/c-api/apiabiversion.html#c.PY_VERSION_HEX for the format of PY_VERSION_HEX.