Jarkko's How to build Configure tweaked by Nick.

The Configure script and config_h.SH file in the Perl distribution are
generated by a program called metaconfig.  Metaconfig was originally 
written by Larry Wall, and was subsequently enhanced and maintained
by Raphael Manfredi.

You have presumably obtained the metaconfig from the repository e.g.
  p4 sync //depot/metaconfig/...
(those are three literal dots) or some other way to obtain this file,
like a complete compressed archive from the previous pumpkin.

Normally this directory and perl directory are next to each other
so ../perl will get you to perl and ../perl/../metaconfig will get you
back here.

Contents of this directory:

    README:	This file.
    U:		Metaconfig units used for buliding Perl's Configure
    U.check:	Sample directory used for testing new metaconfig units.
    		see U.check/README for more information.
    dist-3.0at70: 
    		dist-3.0 at patchlevel 70.  This is the final version released
    		by Raphael Manfredi.  Don't use it.  Instead, use ...
    dist-3.0at70b:
    		dist-3.0 at patchlevel 70 with unofficial patches 'a' and 'b'
		applied.  This version was never officially released, but
		the patches are essential, so this is the version we use for 
		perl.  Actually, I've also applied U/dist_patches/dist-p70c
		to this tree.  If someone with perforce access wants to change
		the name of the directory, that'd be fine.  Otherwise, it really 
		doesn't matter.

(a) You need to have dist installed so that you have metalint and metaconfig
    in your $PATH.
    The dist version used for perl is dist-3.0at70b in this directory.
    Unsurprisingly 'dist' uses (its) Configure to generate itself:

    cd dist-3.0at70b
    chmod +w -R .     # We have derived files in perforce :-(
    ./Configure
    make
    make install

    dist's 'Configure' is similar to perl's but perhaps not
    quite as polished.

    There are some perl specific "dist units" in the 'U' directory.
    The U directory also contains some patches to 'dist' which
    have already been applied to dist-3.0at70b directory.
    We have not yet arranged for metaconfig to use perl's versions
    of the 'units' by default so you need some housekeeping
    in the perl directory...

(b) You need to be in a/the Perl directory, i.e. either
    something from //depot/perl/... or one of its branches
    (e.g. Nick I-S is usually in //depot/perlio/...)
    and you need:
     1) have a symlink to ../metaconfig/U called U
     2) have a symlink to ../metaconfig/.package called .package
     3) have a symlink to MANIFEST called MANIFEST.new
     4) chmod +w Configure config_h.SH Porting/Glossary Porting/config*

(c) Write the new unit as U/foo/bar.U (usually 'foo' is just 'perl',
    but sometimes there's some more appropriate subdir of U.  See
    U/README for a description of the various subdirectories.)

(d) Run metalint to see nits: as opposed to lint, the gripings of
    metalint are usually serious :-) and need fixing

    Exceptions are lots of
      Your private U/modified/voidflags.U overrides the public one.
    due to the perl special units

    and

    "End.U": stale ?MAKE: dependency '$W'.

    which is apparently normal ...

(e) p4 edit Configure config_h.SH

(f) metaconfig -m to regenerate Configure

(g) The messy not-yet-automated part is that the knowledge of the new symbol
    needs to be propagated to non-Configure lands like Win32, WinCE, Netware,
    VMS, VOS, EPOC, ...  see previous Configure changes to see which are these
    heathen lands.  Files to take care of are
    {win32,wince,NetWare}/config_[hH]*, (Win32, WinCE, NetWare),
    configure.com (VMS), VOS/config* (since 5.9 VOS uses Configure, though),
    epoc/config.sh (EPOC).  Depending on the kind of patch djgpp/config*
    might also need adjusting (for example when adding/changing the list
    of extensions)

    For Win32 the process is semi-automated - if you have a Win32
    machine to run dmake on ...

(h) Edit U/mkglossary (right near the top) to point to where you keep
    dist's standard metaconfig units as well as your perl-specific ones.

(i) Run U/mksample to freshen the Porting/config* and Porting/Glossary.
    Adjust the various compile-time options (e.g. 64bit, threads) as
    you see fit.
    You can skip this phase, it's not essential, just good housekeeping.

(j) make veryclean;sh Configure -des -Dusedevel;make all test

(k) p4 add ../metaconfig/foo/bar.U when you are ready ...

(l) p4 submit
    IF your $EDITOR and/or $VISUAL start a background edit session
    ('elvis -fork' or 'gvim'), be sure to set $P4EDITOR to an
    editor call that is waited for.