Fixes "multiple definition" errors when building with GCC 10+.

Based on <https://bugs.gentoo.org/show_bug.cgi?id=706706>.
--- a/fig2dev/dev/gensvg.c	2010-07-01 22:41:16.000000000 +0200
+++ b/fig2dev/dev/gensvg.c	2022-02-27 20:02:33.379945500 +0100
@@ -230,10 +230,12 @@
 };
 
 /* arrowhead arrays */
-Point   points[50], fillpoints[50], clippoints[50];
-int     npoints, nfillpoints, nclippoints;
-int     arrowx1, arrowy1;	/* first point of object */
-int     arrowx2, arrowy2;	/* second point of object */
+Point   fillpoints[50];
+int     nfillpoints;
+extern Point   points[50], clippoints[50];
+extern int     npoints, nclippoints;
+extern int     arrowx1, arrowy1;	/* first point of object */
+extern int     arrowx2, arrowy2;	/* second point of object */
 
 static int tileno=0; /* number of current tile */ 
 
--- a/fig2dev/fig2dev.h	2010-03-16 19:53:20.000000000 +0100
+++ b/fig2dev/fig2dev.h	2022-02-27 19:56:06.072253991 +0100
@@ -126,7 +126,7 @@
 extern char	*prog, *from, *to;
 extern char	*name;
 extern double	font_size;
-Boolean	correct_font_size;	/* use correct font size */
+extern Boolean	correct_font_size;	/* use correct font size */
 extern double	mag, fontmag;
 extern FILE	*tfp;
 
scm'>log</a><a href='/guix/tree/gnu/services/admin.scm?id=a81a64492fbf0ab25b87205850c9f0cd13e6b656'>tree</a><a href='/guix/commit/gnu/services/admin.scm?id=a81a64492fbf0ab25b87205850c9f0cd13e6b656'>commit</a><a href='/guix/diff/gnu/services/admin.scm?id=a81a64492fbf0ab25b87205850c9f0cd13e6b656'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/services/admin.scm'>
<input type='hidden' name='id' value='a81a64492fbf0ab25b87205850c9f0cd13e6b656'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=a81a64492fbf0ab25b87205850c9f0cd13e6b656'>root</a>/<a href='/guix/log/gnu?id=a81a64492fbf0ab25b87205850c9f0cd13e6b656'>gnu</a>/<a href='/guix/log/gnu/services?id=a81a64492fbf0ab25b87205850c9f0cd13e6b656'>services</a>/<a href='/guix/log/gnu/services/admin.scm?id=a81a64492fbf0ab25b87205850c9f0cd13e6b656'>admin.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/services/admin.scm?id=a81a64492fbf0ab25b87205850c9f0cd13e6b656&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-07-27 12:06:36 +0200'>2020-07-27</span></td><td><a href='/guix/commit/gnu/services/admin.scm?id=79501f26ab6d82c0256ff786a5dfb0000b52ccd3'>services: Add 'unattended-upgrade-service-type'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-05-06 11:03:39 +0200'>2020-05-06</span></td><td><a href='/guix/commit/gnu/services/admin.scm?id=ab034adfe86333fccd6afe476806f169e2074d69'>services: rottlog: Append '.gz' to rotated file.</a><span class='msg-avail'>...</span></td><td>Brice Waegeneire</td></tr>
<tr><td><span title='2019-06-15 18:15:23 +0200'>2019-06-15</span></td><td><a href='/guix/commit/gnu/services/admin.scm?id=f3d797005374e5333c7596fe86b4a524ab1b9b11'>services: Remove unneeded imports that led to cycles.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-12-23 17:57:06 +0100'>2018-12-23</span></td><td><a href='/guix/commit/gnu/services/admin.scm?id=83715a7eec81f41a4163a3230d0d8bbbfeb0a5ed'>services: Fix typo in (gnu services admin).</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2018-10-04 09:32:51 +0200'>2018-10-04</span></td><td><a href='/guix/commit/gnu/services/admin.scm?id=89fdd9ee0cc8817283449b33a8c1a2604c575c7e'>services: rottlog: Use command strings in the mcron jobs.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-09-10 12:12:50 +0200'>2018-09-10</span></td><td><a href='/guix/commit/gnu/services/admin.scm?id=19de8273eefceac1ba6ddc8d7e374a13f57c678b'>services: tailon: Move to (gnu services web).</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-03-22 11:43:30 +0100'>2018-03-22</span></td><td><a href='/guix/commit/gnu/services/admin.scm?id=ca5b73114f13e6f34ded3c415721939c196e07dd'>gnu: shepherd: Update to 0.4.0.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-03-22 11:43:29 +0100'>2018-03-22</span></td><td><a href='/guix/commit/gnu/services/admin.scm?id=7fe1432a2ec2b8a7dfbfe882044dadadccd2e2c8'>services: rottlog: Add /var/log/debug to '%default-rotations'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-11-05 15:29:52 +0100'>2017-11-05</span></td><td><a href='/guix/commit/gnu/services/admin.scm?id=21b71b01e9c2264c31ef30451c152bb38cc9e635'>services: Add 'description' fields.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-08-09 23:50:35 +0100'>2017-08-09</span></td><td><a href='/guix/commit/gnu/services/admin.scm?id=101205662588f033c944034f91e7d3cda06d6e56'>services: admin: Simplify the handling of the Tailon debug? option.</a><span class='msg-avail'>...</span></td><td>Christopher Baines</td></tr>
<tr><td><span title='2017-08-09 23:50:31 +0100'>2017-08-09</span></td><td><a href='/guix/commit/gnu/services/admin.scm?id=91fdc8a574cccecd55d042bc1f76ab7f7d3adced'>services: Update the Tailon service for Tailon 1.3.0.</a><span class='msg-avail'>...</span></td><td>Christopher Baines</td></tr>
<tr><td><span title='2017-08-09 23:50:27 +0100'>2017-08-09</span></td><td><a href='/guix/commit/gnu/services/admin.scm?id=f2d8e7f720c92dfb0f49d61f7b66d45e3e63e4cd'>services: Add missing wrap-lines option to tailon.</a><span class='msg-avail'>...</span></td><td>Christopher Baines</td></tr>
<tr><td><span title='2017-07-29 12:45:03 +0100'>2017-07-29</span></td><td><a href='/guix/commit/gnu/services/admin.scm?id=730ed6ec8b69a0f908a8aadbbe0555dd45de227c'>gnu: services: admin: Add tailon.</a><span class='msg-avail'>...</span></td><td>Christopher Baines</td></tr>