Preparing to build Emacs:
You must have a working copy of MMK (MadGoat Make) or MMS (part of DECSet).  I
use MMK.  There are binaries available for both Alpha and Itanium.

If you are using MMK, you must override the MMS symbol to point to it, as part
of the Emacs build process will attempt to invoke MMS:
$ mms == "''mmk'"  ! this assumes you already have an appropriate mmk symbol

After extracting the files from the zipfile, you must define a root "AXPA" that
points to this tree.  For example:
$  define /tran=(conc,term) /job axpa $1$dga3001:[fds0.emilkie.emacs.]


Directory structure:

(root)
  EMACS
    AC   (autoconf for VMS)
    BUILD    <- run all commands while in this directory
      LISP
      LWLIB   (x-windows obj's appear here)
      OLDXMENU (x-windows obj's appear here)
      SRC     (emacs obj's appear here)
      TRADCPP (C preprocessor used to preprocess DESCRIP.MMS_IN_IN)
      VMS  (here is where the build products appear, e.g. TEMACS.EXE)
    EMACS212_3 (all emacs source files live within here)
      LISP
      LWLIB     (x-windows source)
      OLDXMENU (x-windows source)
      SRC (Main Emacs source directory!)
        M (machine-specific header files)
        S (os-specific header files)
      TRADCPP (same as in BUILD)
      VMS (helper VMS utilities to help Emacs build)
  PLAY


Files of note:
AXPA:[EMACS.EMACS212_3.SRC]DESCRIP.MMS_IN_IN
Edit this file to adjust how things are built and linked.  This file becomes
AXPA:[EMACS.BUILD]DESCRIP.MMS when you run "configure".

AXPA:[EMACS.BUILD.VMS]TEMACS.EXE
This is the emacs executable.  When you run "mmk install", it gets renamed to
EMACS-21_2.EXE.

AXPA:[EMACS.BUILD.VMS]TEMACS_D.EXE
This is the emacs executable if you build it in debug mode by using "mmk debug".

AXPA:[EMACS.BUILD.VMS]TEMACS.DUMP
This is the dumpfile that is created at the end of emacs build.  It contains
the program sections from virtual memory that are memory-mapped when Emacs is
started.

Building Emacs:

0. Build TRADCPP
You may need to rebuild TRADCPP if it gives errors during the build. Simply
change to its directory and do "mmk".  You should only need to do this once.

1. Run configure.
Change default directory to AXPA:[EMACS.BUILD].  Run configure:
$ @[-.emacs212_3]configure --with-tcpip=YES --with-x=YES --prefix=AXPA:[LOCAL]
--startupdir=AXPA:[LOCAL.STARTUP]

You can get a list of options that configure takes by giving the -h option.  We
use Multinet at FactSet so the descrip.mms file may try to link against only
Multinet libraries.  It should also be able to use TCP/IP Services libraries,
however.
After configure runs, it should parse
AXPA:[EMACS.EMACS212_3.SRC]DESCRIP.MMS_IN_IN and produce
AXPA:[EMACS.BUILD]DESCRIP.MMS.

2. Run MMK.
With a proper descrip.mms file, run:
$ mmk /ignore=warn
You may wish to run $ mmk clean first if you have changed descrip.mms_in_in.
Emacs will build.  The build may fail to find a header file; if this occurs,
simply invoke mmk again.  There is a bug with either mmk or the descrip.mms
file in that it changes directories to build oldxmenu but for some reason
doesn't restore the directory when it moves on to build emacs files.
After emacs is built and links, it will invoke emacs in batch mode in order to
"dump" it.  You will see many messages about loading various Lisp modules, then
it will produce a TEMACS.DUMP file.

3. Test emacs
To run a test, invoke:
$ mcr [.vms]temacs.exe -map [.vms]temacs.dump

Building Emacs in Debug mode
To build emacs in debug mode for use with the debugger, change the file
AXPA:[EMACS.EMACS212_3.SRC.S]VMS.H
Find the declaration of C_DEBUG_SWITCH and change it to be /deb/noopt
Rerun configure.
Invoke mmk as:
$ mmk debug /ignore=warn
Note that the image will be created with the name TEMACS_D.EXE, so to run it
you will use:
$ mcr [.vms]temacs_d.exe -map [.vms]temacs.dump

Important files
VMSMAP.C in the emacs SRC directory:
Contains the code to "dump" emacs when it is built, and also to map in the
sections from the dump file when Emacs is run.
VMSGMALLOC.C:
Contains the custom memory allocator for Emacs; adapted from the original GNU
malloc/free.

Helpful website
http://www.delorie.com/gnu/docs/elisp-manual-21/elisp_715.html
(from the GNU Emacs manual)
This webpage describes how the Emacs dumping process is undertaken.

Installing Emacs
Normally, after emacs is built, one runs 
$ mmk install /ign=warn
And files are copied out to the location specified in the --prefix when you
first ran configure.  At this point, the temacs.exe file is renamed and placed
in a production location for users.