Integrate perlio:

Integrate perlio:

[ 16367]
Several of non-default builds now seem to work reasonably well
English.t seems to fail on an errno test, and socketpair blathers
about something.
Basic fix is to stop PERL_IMPLICIT_SYS turning on USE_PERLIO by the
back door, and instead have perlsdio.h vector stdio via iperlsys.h
function tables (latter was done in earlier change).
Update comments in Makefile.mk

[ 16366]
Finish off 16350 for non-PERLIO build on linux,
non PERL_IMPLICIT_SYS parts of iperlsys.h had junk
for some slots which now perlsdio.h is targeting.

[ 16352]
setbuf / setvbuf are not PerlIO_ concepts

[ 16351]
perl_clone is a threads thing

[ 16350]
*** EXPERIMENTAL ***
Have perlsdio.h use the iperlsys.h aliases and see
if that helps non-PERLIO IMP_SYS on Win32.
(Miniperl okay on linux).

[ 16349]
Win32 builds and mostly works for non-USE_PERLIO non-USE_IMP_SYS case.
- move body of fdupopen() from perlhost.h to win32.h as win32_fdupopen()
- use it in perlio.c

[ 16347]
More layer syms

[ 16346]
Use PerlSIO_fdupopen() if not using PerlIO

[ 16345]
Do not build if not using layers
p4raw-link: @16367 on //depot/perlio: 2cbbe5a150b07f176547702112505e3d30ea082f
p4raw-link: @16366 on //depot/perlio: 079b94bc698b0934beaf07d168872e7ff53ba831
p4raw-link: @16352 on //depot/perlio: 22a46b6e190a186151dafce1a1c165a2532b0f1d
p4raw-link: @16351 on //depot/perlio: 0295eab83c15497fe4260ac4facad25c962a4293
p4raw-link: @16350 on //depot/perlio: 362d0d4483498690d9657a76e53755c85da3b796
p4raw-link: @16349 on //depot/perlio: 30753f56c8bbfb209552e904d9d76202413ebf24
p4raw-link: @16347 on //depot/perlio: 1e8a8f599308436d6e164543b54e022d0b1a9177
p4raw-link: @16346 on //depot/perlio: 0553478ef48e094f904ff993d3c57b7325174272
p4raw-link: @16345 on //depot/perlio: 57143e73be61ad4ed95e8d5fdc799945c48c8339

p4raw-id: //depot/perl@16368