genpacksizetables.pl: Correct comment typo
Propagate a change from commit 1651fc447620d361 into genpacksizetables.pl.

pp_pack.c contains a table generated by genpacksizetables.pl, pasted into the
C source. The C source was updated by commit 1651fc447620d361 in April 2007,
but the table used to generate the code was not.
Extract the generated packprops array into packsizetables.c.

The C source is the output from genpacksizetables.pl
Previously it was pasted into pp_pack.c

 LocalWords:  packprops
Refactor genpacksizetables.pl to use regen/regen_lib.pl
Move genpacksizetables.pl to regen/genpacksizetables.pl
Add regen/genpacksizetables.pl to t/porting/regen.t
Eliminate pre-5.9.x conditional code for PERL_PACK_CAN_BYTEORDER

PERL_PACK_CAN_BYTEORDER has been unconditionally defined for versions 5.9.x
and greater, and undefined for 5.8.x. As we are never going to need to
port changes back to maint-5.8 any more, eliminate all the 5.8.x related code,
and the macro that supports it.
Eliminate pre-5.9.x conditional code for PERL_PACK_CAN_SHRIEKSIGN

PERL_PACK_CAN_SHRIEKSIGN has been unconditionally defined for versions 5.9.x
and greater, and undefined for 5.8.x. As we are never going to need to
port changes back to maint-5.8 any more, eliminate all the 5.8.x related code
and the macro that supports it.
Eliminate the definitions for DO_BO_PACK_P and DO_BO_UNPACK_P.

Commit 07409e015252427f in April 2005 replaced all the uses of these two
macros with DO_BO_PACK_PC and DO_BO_UNPACK_PC.
vtohl, vtohs, htovl and htovs are no-ops on 64 bit little endian systems.

Previously they were implemented as function calls on 64 bit little endian
systems. Bit endian systems implemented them as byte-swapping macros. 32
little endian system didn't implement them at all. 32 and 64 bit little
endian systems now behave identically.
Provide vtohl, vtohs, htovl and htovs no-op macros on little endian systems.

This means that there are always macros or functions for vtohl, vtohs,
htovl and htovs available, so eliminate HAS_VTOHL etc, and unconditionally
compile the code that it was protecting. grep.cpan.me shows that no code on
CPAN uses any of these macros.

(Technically the 4 are not quite no-ops, as they truncate their values to
32 or 16 bits, to be consistent with the implementations for platforms which
need re-ordering.)
Provide ntohl, ntohs, htonl and htons no-op macros on big endian systems.

This means that there are always macros or functions for ntohl, ntohs,
htonl and htons available, so eliminate use of HAS_NTOHL etc, and
unconditionally compile the code that it was protecting. However, as code
on CPAN is using these guard macros, define all of them in perl.h

(Technically the 4 are not quite no-ops, as they truncate their values to
32 or 16 bits, to be consistent with the implementations for platforms which
need re-ordering.)