dist/IO.xs remove a dTHX call

- threaded perls without CPerlHost/iperlsys.h (ie all threaded unix perls)
  dont need a my_perl ptr, and don't assume all CCes have perfect LTO/LTCG
  and all OSes have a perfect designed bin image loader, to optimize away
  an unused my_perl var. This symbol crosses 2 separate TUs.
  ELF interposition, on paper, doesn't allow shifting over and dropping
  out args, but in real life, things are probably different. Write it
  correctly than assume optimizations will happen.

Author: bulk88

dist/IO/ChangeLog

@@ -1,3 +1,7 @@
+IO 1.56
+    * A very minor optimization was done in perl's emulated poll() on the OSes
+      that use need that use Perl's implementation.
+
 IO 1.55
     * XS changes for getline/getlines to support reference counted stacks
     * moved the binmode method from IO::File to IO::Handle, since all types

dist/IO/IO.pm

@@ -7,7 +7,7 @@ use Carp;
 use strict;
 use warnings;
 
-our $VERSION = "1.55";
+our $VERSION = "1.56";
 XSLoader::load 'IO', $VERSION;
 
 sub import {

dist/IO/poll.c

@@ -10,6 +10,7 @@
  *
  */
 
+#define PERL_NO_GET_CONTEXT
 #include "EXTERN.h"
 #include "perl.h"
 #include "XSUB.h"
@@ -40,8 +41,13 @@
 
 # define POLL_EVENTS_MASK (POLL_CAN_READ | POLL_CAN_WRITE | POLL_HAS_EXCP)
 
+#if defined(PERL_IMPLICIT_SYS)
 int
-poll(struct pollfd *fds, unsigned long nfds, int timeout)
+Perl_my_poll_cxt(pTHX_ struct pollfd *fds, unsigned long nfds, int timeout)
+#else
+int
+Perl_my_poll(struct pollfd *fds, unsigned long nfds, int timeout)
+#endif
 {
     int i,err;
     fd_set rfd,wfd,efd,ifd;

dist/IO/poll.h

@@ -29,7 +29,12 @@
 #ifdef poll
 # undef poll
 #endif
-#define poll Perl_my_poll
+
+#if defined(PERL_IMPLICIT_SYS)
+#  define poll(_fds, _nfds, _tm) Perl_my_poll_cxt(aTHX_ _fds, _nfds, _tm)
+#else
+#  define poll Perl_my_poll
+#endif
 
 #if WINVER < 0x0600
 typedef struct pollfd {
@@ -55,7 +60,11 @@ typedef struct pollfd {
 
 #endif
 
-int poll (struct pollfd *, unsigned long, int);
+#if defined(PERL_IMPLICIT_SYS)
+  int Perl_my_poll_cxt(pTHX_ struct pollfd *, unsigned long, int);
+#else
+  int Perl_my_poll(struct pollfd *, unsigned long, int);
+#endif
 
 #ifndef HAS_POLL
 #  define HAS_POLL