Disable XS prototypes by default

When neither -prototypes not -noprototypes is passed to xsubpp, it will
require the XS files to contain a PROTOTYPES statement. This is a
compatibility feature that dealt with a breaking change in 1996, it long
stopped having any purpose. Module::Build has disabled it since the very
first version that supported XS (0.03 in 2001), and so should we.

Author: Leont

lib/ExtUtils/MM_Unix.pm

@@ -3967,7 +3967,7 @@ sub tool_xsubpp {
     }
 
 
-    $self->{XSPROTOARG} = "" unless defined $self->{XSPROTOARG};
+    $self->{XSPROTOARG} = "-noprototypes" unless defined $self->{XSPROTOARG};
     $self->tool_xsubpp_emit($xsdir, \@tmdeps, \@tmargs);
 }