Fix build failure on glibc 2.28 where 'renameat2' would end up being
declared twice: <https://github.com/systemd/casync/issues/166>.

From 625244ca47e8ee1375d2d0092271bfd13b0913ea Mon Sep 17 00:00:00 2001
From: Daniel Mack <daniel@zonque.org>
Date: Tue, 13 Nov 2018 17:52:48 +0100
Subject: [PATCH] meson.build: pass -D_GNU_SOURCE when checking for functions

As described in #166, -D_GNU_SOURCE needs to be passed to the meson function
availability checker. h/t to @tomeon for providing a link to the solution as
well.
---
 meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/meson.build b/meson.build
index f42ed16..c0f741e 100644
--- a/meson.build
+++ b/meson.build
@@ -78,6 +78,6 @@ foreach ident : [
         ['copy_file_range',   '''#include <sys/syscall.h>
                                  #include <unistd.h>'''],
 ]
-        have = cc.has_function(ident[0], prefix : ident[1])
+        have = cc.has_function(ident[0], args : '-D_GNU_SOURCE', prefix : ident[1])
         conf.set10('HAVE_' + ident[0].to_upper(), have)
 endforeach
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<div class='path'>path: <a href='/guix/log/?id=4621cd7b8db00fd8230c8c5e51929f926aaf3795'>root</a>/<a href='/guix/log/doc?id=4621cd7b8db00fd8230c8c5e51929f926aaf3795'>doc</a>/<a href='/guix/log/doc/images?id=4621cd7b8db00fd8230c8c5e51929f926aaf3795'>images</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/doc/images?id=4621cd7b8db00fd8230c8c5e51929f926aaf3795&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-05-22 16:11:52 +0200'>2020-05-22</span></td><td><a href='/guix/commit/doc/images?id=cd5d5f53228fd5bf96d9f790aa2606ae71fa68d7'>doc: Update 'Bootstrapping' for further binary seed reduction.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/images/gcc-core-mesboot0-graph.dot: New image, replacing
* doc/images/gcc-mesboot0-bag-graph.dot: ... remove file.
* doc/local.mk (DOT_FILES): Update for new image file.
* doc/guix.texi (Reduced Binary Seed Bootstrap): Use it in updated description
of further reduction of the trusted computing base.
</span></span></td><td>Jan Nieuwenhuizen</td></tr>
<tr><td><span title='2019-03-14 16:30:19 +0100'>2019-03-14</span></td><td><a href='/guix/commit/doc/images?id=19008a22d18e772062952034c58a15ed341df3b5'>Merge branch 'staging' into core-updates</a></td><td>Marius Bakke</td></tr>
<tr><td><span title='2019-03-13 23:12:43 +0100'>2019-03-13</span></td><td><a href='/guix/commit/doc/images?id=e1c15e8b8e25e14c253ff1212e289565736f6ea7'>doc: Document the graphical installer some more.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/guix.texi (Preparing for Installation): Rewrite to specify the two
installation modes.
(Guided Graphical Installation): New node.
(Manual Installation): New node, with the former sections.
(After System Installation): New node.
* doc/images/installer-network.png, doc/images/installer-partitions.png,
doc/images/installer-resume.png: New files.
* doc/local.mk (dist_infoimage_DATA): Add them.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-12-16 22:49:10 +0100'>2018-12-16</span></td><td><a href='/guix/commit/doc/images?id=b3bf38a5600d0fdcb0aeed29ee121edef632165d'>doc: Update mesboot graph without bootstrap-guile.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/images/gcc-mesboot-bag-graph.dot: Update.
</span></span></td><td>Jan Nieuwenhuizen</td></tr>
<tr><td><span title='2018-11-24 08:18:31 +0100'>2018-11-24</span></td><td><a href='/guix/commit/doc/images?id=3d3daf7fa1794c64914ed53e51838a41d9b7adc4'>doc: Update for bootstrap-mescc-tools change.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/guix.texi (Reduced Binary Seed Bootstrap): Update for
bootstrap-mescc-tools change.
* doc/images/gcc-mesboot-bag-graph.dot: Regenerate.
</span></span></td><td>Jan Nieuwenhuizen</td></tr>
<tr><td><span title='2018-09-23 09:46:26 +0200'>2018-09-23</span></td><td><a href='/guix/commit/doc/images?id=a243722c5b8d50b4f0e3f9717ca71aa43dfc56a3'>doc: Describe the Reduced Binary Seed bootstrap.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/guix.texi (Reduced Binary Seed Bootstrap): New node.
* doc/images/gcc-mesboot-bag-graph.dot: New file.
* doc/local.mk (DOT_FILES): Add it.
</span></span></td><td>Jan Nieuwenhuizen</td></tr>
<tr><td><span title='2016-12-17 14:46:42 +0100'>2016-12-17</span></td><td><a href='/guix/commit/doc/images?id=aaee461b9d5fb85fc1a548877dc7eea3dd4fbf50'>doc: Update dot graphs.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/images/bootstrap-packages.dot,
doc/images/coreutils-bag-graph.dot, doc/images/coreutils-graph.dot,
doc/images/shepherd-graph.dot: Regenerate.
</span></span></td><td>Ludovic Courtès</td></tr>