preprocessor: Fix non-fn fn-like macro at EOF [PR97471]
We inject EOF tokens between macro argument lists, but had
confused/stale logic in the non-fn invocation. Renamed the magic
'eof' token, as it's now only used for macro argument termination.
Always rewind the non-OPEN_PAREN token.
libcpp/
* internal.h (struct cpp_reader): Rename 'eof' field to 'endarg'.
* init.c (cpp_create_reader): Adjust.
* macro.c (collect_args): Use endarg for separator. Always rewind
in the not-fn case.
gcc/testsuite/
* c-c++-common/cpp/pr97471.c: New.