Use the same $func to Perl_$func macros independent of multiplicity.

Use the same $func to Perl_$func macros independent of multiplicity.

The macros of the form #define foo(a, b) Perl_foo(aTHX_ a, b) will also work
under non-multiplicity. There's no issue with adding explicit arguments in
the non-multiplicity case, because it changes one form of compile-time error
into another. (Function Perl_foo passed the wrong number of arguments into
macro foo passed the wrong number of arguments.)