Avoid "multiple definition of `mystruct'" error from `ld`:

Submitted upstream at https://github.com/idris-lang/Idris-dev/issues/4914

--- a/test/ffi008/ffi008.h	1969-12-31 18:00:01.000000000 -0600
+++ a/test/ffi008/ffi008.h	2022-04-13 00:32:35.561262598 -0500
@@ -10,7 +10,7 @@
     int16_t b;
 };
 
-struct test2 mystruct;
+extern struct test2 mystruct;
 
 int size1(void);
 int size2(void);
--- a/test/ffi008/ffi008.c	1969-12-31 18:00:01.000000000 -0600
+++ a/test/ffi008/ffi008.c	2022-04-13 00:32:53.145186302 -0500
@@ -11,6 +11,8 @@
     return sizeof(struct test2);
 }
 
+struct test2 mystruct;
+
 void print_mystruct(void) {
     printf("a: %d b: %d\n", mystruct.a, mystruct.b);
 }
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<tr><td><span title='2022-09-22 16:00:29 +0200'>2022-09-22</span></td><td><a href='/guix/commit/gnu/installer/user.scm?id=4814ec284f8a2870e6457c05f414ad31df4e3f57'>installer: Move &lt;secret&gt; to utils and use it for crypt passwords.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/installer/user.scm (&lt;secret&gt;, secret?, make-secret, secret-content): Move
to utils.scm.
* gnu/installer/utils.scm (&lt;secret&gt;, secret?, make-secret, secret-content):
Moved from user.scm.
* gnu/installer/newt/partition.scm (prompt-luks-passwords): Make password a
&lt;secret&gt;.
* gnu/installer/parted.scm (luks-format-and-open): Unwrap secret.

Signed-off-by: Mathieu Othacehe &lt;othacehe@gnu.org&gt;
</span></span></td><td>Josselin Poiret</td></tr>
<tr><td><span title='2022-08-08 11:54:25 +0200'>2022-08-08</span></td><td><a href='/guix/commit/gnu/installer/user.scm?id=ff9522fb69b9f4a31a5b766029e26dc53a2d1cf8'>installer: Add comments and vertical space to the generated config.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/installer/parted.scm (user-partitions-&gt;configuration): Introduce
vertical space and a comment.
* gnu/installer/services.scm (G_): New macro.
(%system-services): Add comment for OpenSSH.
(system-services-&gt;configuration): Add vertical space and comments.
* gnu/installer/user.scm (users-&gt;configuration): Add comment.
* gnu/installer/steps.scm (format-configuration): Add comment.
(configuration-&gt;file): Expound leading comment.  Pass #:format-comment
to 'pretty-print-with-comments/splice'.
</span></span></td><td>Ludovic Courtès</td></tr>