improve description of how "build.sh -m mach" sets the default

MACHINE_ARCH, and list the special cases that this does not occur for.

BUILDING

@@ -534,9 +534,25 @@ BUILDING
 
      -m mach   Set the value of MACHINE to mach.  This will also override any
                value of MACHINE_ARCH in the process environment with a value
-               deduced from mach, unless -a is specified.  All cross builds
-               require -m, but if unset on a NetBSD host, the host's value of
-               MACHINE will be detected and used automatically.
+               deduced from mach, unless -a is specified, or mach is a special
+               case listed below.  All cross builds require -m, but if unset
+               on a NetBSD host, the host's value of MACHINE will be detected
+               and used automatically.
+
+               Some machines support multiple values for MACHINE_ARCH.  For a
+               given value of mach, the following MACHINE and MACHINE_ARCH
+               values will result:
+
+                     mach          MACHINE    MACHINE_ARCH
+                     evbmips       evbmips    (not set)
+                     evbmips-eb    evbmips    mipseb
+                     evbmips-el    evbmips    mipsel
+                     evbsh3        evbsh3     (not set)
+                     evbsh3-eb     evbsh3     sh3eb
+                     evbsh3-el     evbsh3     sh3el
+                     sbmips        sbmips     (not set)
+                     sbmips-eb     sbmips     mipseb
+                     sbmips-el     sbmips     mipsel
 
      -n        Show the commands that would be executed by build.sh, but do
                not make any changes.  This is similar in concept to ``make
@@ -626,4 +642,4 @@ HISTORY
 BUGS
      A few platforms are not yet using this build system.
 
-NetBSD                           May 10, 2003                               10
+NetBSD                           May 17, 2003                               10

doc/BUILDING.mdoc

@@ -1,4 +1,4 @@
-.\"	$NetBSD: BUILDING.mdoc,v 1.19 2003/05/10 07:15:52 lukem Exp $
+.\"	$NetBSD: BUILDING.mdoc,v 1.20 2003/05/17 08:10:39 lukem Exp $
 .\"
 .\" Copyright (c) 2001-2003 The NetBSD Foundation, Inc.
 .\" All rights reserved.
@@ -40,7 +40,7 @@
 .\" Toolchain prefix for commands
 .ds toolprefix nb
 .
-.Dd May 10, 2003
+.Dd May 17, 2003
 .Dt BUILDING 8
 .Os NetBSD
 .
@@ -1036,11 +1036,35 @@ in the process environment with a value deduced from
 .Ar mach ,
 unless
 .Fl a
-is specified.
+is specified, or
+.Ar mach
+is a special case listed below.
 All cross builds require
 .Fl m ,
 but if unset on a NetBSD host, the host's value of MACHINE will be
 detected and used automatically.
+.Pp
+Some machines support multiple values for
+.Sy MACHINE_ARCH .
+For a given value of
+.Ar mach ,
+the following
+.Sy MACHINE
+and
+.Sy MACHINE_ARCH
+values will result:
+.Bl -column "evbmips-el" "MACHINE" "MACHINE_ARCH" -offset indent
+.It Sy Ar mach Ta Sy "MACHINE" Ta Sy "MACHINE_ARCH"
+.It evbmips Ta evbmips Ta (not set)
+.It evbmips-eb Ta evbmips Ta mipseb
+.It evbmips-el Ta evbmips Ta mipsel
+.It evbsh3 Ta evbsh3 Ta (not set)
+.It evbsh3-eb Ta evbsh3 Ta sh3eb
+.It evbsh3-el Ta evbsh3 Ta sh3el
+.It sbmips Ta sbmips Ta (not set)
+.It sbmips-eb Ta sbmips Ta mipseb
+.It sbmips-el Ta sbmips Ta mipsel
+.El
 .
 .It Fl n
 Show the commands that would be executed by