[man pages]: Define page-local `MR` fallback.

[man pages]: Provide page-local fallback definition of new `MR` macro.
I didn't think I was going to have to do this, but the premier site on
the web for viewing Linux man pages, Michael Kerrisk's man7.org, has
been pulling snapshots of the pages themselves without upgrading the
underlying macros, and so man page cross references set with `MR` are
getting lost in its presentations.  (I acknowledge: Ingo Schwarze warned
me something like this could happen.)  This definition is intended as a
stopgap measure only.  I want to revert this after groff 1.23 is
released and has spread to some reasonable degree.

* contrib/chem/chem.1.man:
* contrib/eqn2graph/eqn2graph.1.man:
* contrib/gdiffmk/gdiffmk.1.man:
* contrib/glilypond/glilypond.1.man:
* contrib/gperl/gperl.1.man:
* contrib/gpinyin/gpinyin.1.man:
* contrib/grap2graph/grap2graph.1.man:
* contrib/hdtbl/groff_hdtbl.7.man:
* contrib/mm/groff_mm.7.man:
* contrib/mm/groff_mmse.7.man:
* contrib/mm/mmroff.1.man:
* contrib/mom/groff_mom.7.man:
* contrib/pdfmark/pdfroff.1.man:
* contrib/pic2graph/pic2graph.1.man:
* contrib/rfc1345/groff_rfc1345.7.man:
* man/groff.7.man:
* man/groff_char.7.man:
* man/groff_diff.7.man:
* man/groff_font.5.man:
* man/groff_out.5.man:
* man/groff_tmac.5.man:
* man/roff.7.man:
* src/devices/grodvi/grodvi.1.man:
* src/devices/grohtml/grohtml.1.man:
* src/devices/grolbp/grolbp.1.man:
* src/devices/grolj4/grolj4.1.man:
* src/devices/gropdf/gropdf.1.man:
* src/devices/gropdf/pdfmom.1.man:
* src/devices/grops/grops.1.man:
* src/devices/grotty/grotty.1.man:
* src/devices/xditview/gxditview.1.man:
* src/preproc/eqn/eqn.1.man:
* src/preproc/eqn/neqn.1.man:
* src/preproc/grn/grn.1.man:
* src/preproc/pic/pic.1.man:
* src/preproc/preconv/preconv.1.man:
* src/preproc/refer/refer.1.man:
* src/preproc/soelim/soelim.1.man:
* src/preproc/tbl/tbl.1.man:
* src/roff/groff/groff.1.man:
* src/roff/nroff/nroff.1.man:
* src/roff/troff/troff.1.man:
* src/utils/addftinfo/addftinfo.1.man:
* src/utils/afmtodit/afmtodit.1.man:
* src/utils/grog/grog.1.man:
* src/utils/hpftodit/hpftodit.1.man:
* src/utils/indxbib/indxbib.1.man:
* src/utils/lkbib/lkbib.1.man:
* src/utils/lookbib/lookbib.1.man:
* src/utils/pfbtops/pfbtops.1.man:
* src/utils/tfmtodit/tfmtodit.1.man:
* src/utils/xtotroff/xtotroff.1.man:
* tmac/groff_man.7.man.in:
* tmac/groff_me.7.man:
* tmac/groff_ms.7.man:
* tmac/groff_trace.7.man:
* tmac/groff_www.7.man: Do it.

The sed script I used follows.  I patched neqn(1), which does not
require compatibility mode, by hand.

/^\.cp 0/a\
.\
.\\" Define fallback for groff 1.23's MR macro if the system lacks it.\
.de @@\
.  de MR\
.    ie \\n(.$=1 \\\
.      I \%\\$1\
.    el \\\
.      IR \%\\$1 (\\$2)\\$3\
.  \\\\.\
..\
.if  \\n(.g .if !d MR .@@\
.if !\\n(.g .@@\
.rm @@

5 files changed, 65 insertions, 0 deletions

diff --git a/tmac/groff_man.7.man.in b/tmac/groff_man.7.man.in
index 69b5551d1..217acfc97 100644
--- a/tmac/groff_man.7.man.in
+++ b/tmac/groff_man.7.man.in
@@ -83,6 +83,19 @@ _endif()dnl
 .do nr *groff_groff_man_7_man_C \n[.cp]
 .cp 0
 .
+.\" Define fallback for groff 1.23's MR macro if the system lacks it.
+.de @@
+.  de MR
+.    ie \n(.$=1 \
+.      I %\$1
+.    el \
+.      IR %\$1 (\$2)\$3
+.  \\.
+..
+.if  \n(.g .if !d MR .@@
+.if !\n(.g .@@
+.rm @@
+.
 .
 .\" ====================================================================
 .SH Synopsis
diff --git a/tmac/groff_me.7.man b/tmac/groff_me.7.man
index 8b0e0d834..3966e0cb9 100644
--- a/tmac/groff_me.7.man
+++ b/tmac/groff_me.7.man
@@ -52,6 +52,19 @@ documents
 .do nr *groff_groff_me_7_man_C \n[.cp]
 .cp 0
 .
+.\" Define fallback for groff 1.23's MR macro if the system lacks it.
+.de @@
+.  de MR
+.    ie \n(.$=1 \
+.      I %\$1
+.    el \
+.      IR %\$1 (\$2)\$3
+.  \\.
+..
+.if  \n(.g .if !d MR .@@
+.if !\n(.g .@@
+.rm @@
+.
 .
 .\" ====================================================================
 .SH Synopsis
diff --git a/tmac/groff_ms.7.man b/tmac/groff_ms.7.man
index 4fbe8e26c..f9c66c131 100644
--- a/tmac/groff_ms.7.man
+++ b/tmac/groff_ms.7.man
@@ -32,6 +32,19 @@ manuscript macro package for formatting documents
 .do nr *groff_groff_ms_7_man_C \n[.cp]
 .cp 0
 .
+.\" Define fallback for groff 1.23's MR macro if the system lacks it.
+.de @@
+.  de MR
+.    ie \n(.$=1 \
+.      I %\$1
+.    el \
+.      IR %\$1 (\$2)\$3
+.  \\.
+..
+.if  \n(.g .if !d MR .@@
+.if !\n(.g .@@
+.rm @@
+.
 .
 .\" ====================================================================
 .SH Synopsis
diff --git a/tmac/groff_trace.7.man b/tmac/groff_trace.7.man
index 45fbed598..7fbfdcc92 100644
--- a/tmac/groff_trace.7.man
+++ b/tmac/groff_trace.7.man
@@ -27,6 +27,19 @@ documents
 .do nr *groff_groff_trace_7_man_C \n[.cp]
 .cp 0
 .
+.\" Define fallback for groff 1.23's MR macro if the system lacks it.
+.de @@
+.  de MR
+.    ie \n(.$=1 \
+.      I %\$1
+.    el \
+.      IR %\$1 (\$2)\$3
+.  \\.
+..
+.if  \n(.g .if !d MR .@@
+.if !\n(.g .@@
+.rm @@
+.
 .
 .\" ====================================================================
 .SH Synopsis
diff --git a/tmac/groff_www.7.man b/tmac/groff_www.7.man
index 4b34d3eef..7dfe0facc 100644
--- a/tmac/groff_www.7.man
+++ b/tmac/groff_www.7.man
@@ -32,6 +32,19 @@ macros for authoring web pages
 .do nr *groff_groff_www_7_man_C \n[.cp]
 .cp 0
 .
+.\" Define fallback for groff 1.23's MR macro if the system lacks it.
+.de @@
+.  de MR
+.    ie \n(.$=1 \
+.      I %\$1
+.    el \
+.      IR %\$1 (\$2)\$3
+.  \\.
+..
+.if  \n(.g .if !d MR .@@
+.if !\n(.g .@@
+.rm @@
+.
 .
 .\" ====================================================================
 .SH Synopsis