autodoc: Handle pTHX on no-long name functions

There are currently three functions that have an implicit thread context
parameter that don't have long names.  (A long name is prefixed with
'Perl_' or 'S_'.)  Prior to this commit they were displayed in perlapi
without that parameter.

The three are Perl_localeconv, PerlIO_apply_layers, and PerlIO_binmode.

Author: khwilliamson

autodoc.pl

@@ -1839,6 +1839,17 @@ ($fh, $element_name, $docref)
             if ($has_args) {
                 @args = $item->{args}->@*;
 
+                # A thread context parameter is the default for functions (not
+                # macros) unless the T flag is specified.  Those functions
+                # that don't have long names (indicated by not having any of
+                # the [IipS] flags have such an implicit parameter, that we
+                # need to make explicit for the documentation.
+                if ($item->{flags} !~ /[ IipS Mm T ]/xx)  {
+                    $this_has_pTHX = 1;     # This 3 line design pattern is
+                    unshift @args, "pTHX";  # repeated a few lines below
+                    $any_has_pTHX_ = 1 if @args > 1;
+                }
+
                 # If only the Perl_foo form is to be displayed, change the
                 # name of this item to be that.  This happens for either of
                 # two reasons: