Fix a string comparison in C++ 11.

Taken from Debian:
https://sources.debian.org/src/dbus-c++/0.9.0-8.1/debian/patches/06_fix_gcc-7_ftbfs.patch/

--- a/src/pipe.cpp
+++ b/src/pipe.cpp
@@ -83,5 +83,5 @@ ssize_t Pipe::read(void *buffer, unsigne
 void Pipe::signal()
 {
   // TODO: ignoring return of read/write generates warning; maybe relevant for eventloop work...
-  ::write(_fd_write, '\0', 1);
+  ::write(_fd_write, "\0", 1);
 }
<td class='logo' rowspan='2'><a href='/'><img src='https://git.koszko.org/cgit-static/cgit.png' alt='cgit logo'/></a></td>
<td class='main'><a href='/'>index</a> : <a href='/guix/'>guix</a></td><td class='form'><form method='get'>
<input type='hidden' name='id' value='a14a94deb218f459dc8a3139ef6e25f15c822463'/><select name='h' onchange='this.form.submit();'>
<option value='koszko' selected='selected'>koszko</option>
<option value='koszko-scripts'>koszko-scripts</option>
</select> <input type='submit' value='switch'/></form></td></tr>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=a14a94deb218f459dc8a3139ef6e25f15c822463'>refs</a><a class='active' href='/guix/log/gnu/packages/patches/ganeti-relax-dependencies.patch'>log</a><a href='/guix/tree/gnu/packages/patches/ganeti-relax-dependencies.patch?id=a14a94deb218f459dc8a3139ef6e25f15c822463'>tree</a><a href='/guix/commit/gnu/packages/patches/ganeti-relax-dependencies.patch?id=a14a94deb218f459dc8a3139ef6e25f15c822463'>commit</a><a href='/guix/diff/gnu/packages/patches/ganeti-relax-dependencies.patch?id=a14a94deb218f459dc8a3139ef6e25f15c822463'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/packages/patches/ganeti-relax-dependencies.patch'>
<input type='hidden' name='id' value='a14a94deb218f459dc8a3139ef6e25f15c822463'/><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=a14a94deb218f459dc8a3139ef6e25f15c822463'>root</a>/<a href='/guix/log/gnu?id=a14a94deb218f459dc8a3139ef6e25f15c822463'>gnu</a>/<a href='/guix/log/gnu/packages?id=a14a94deb218f459dc8a3139ef6e25f15c822463'>packages</a>/<a href='/guix/log/gnu/packages/patches?id=a14a94deb218f459dc8a3139ef6e25f15c822463'>patches</a>/<a href='/guix/log/gnu/packages/patches/ganeti-relax-dependencies.patch?id=a14a94deb218f459dc8a3139ef6e25f15c822463'>ganeti-relax-dependencies.patch</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/packages/patches/ganeti-relax-dependencies.patch?id=a14a94deb218f459dc8a3139ef6e25f15c822463&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-09-08 18:53:46 +0800'>2023-09-08</span></td><td><a href='/guix/commit/gnu/packages/patches/ganeti-relax-dependencies.patch?id=b41ea5dcd4a70af3b5efdcac939b56a0e2243a69'>gnu: ganeti: Fix build.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/patches/ganeti-lens-compat.patch,
gnu/packages/patches/ganeti-procps-compat.patch,
gnu/packages/patches/ganeti-relax-dependencies.patch,
gnu/packages/patches/ganeti-reorder-arbitrary-definitions.patch,
gnu/packages/patches/ganeti-template-haskell-2.17.patch,
gnu/packages/patches/ganeti-template-haskell-2.18.patch: New files.
* gnu/local.mk (dist_patch_DATA): Adjust accordingly.
* gnu/packages/virtualization.scm (ganeti)[source](patches): Add them.
</span></span></td><td>Marius Bakke</td></tr>