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);
 }
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<tr><td><span title='2020-07-18 21:12:38 +0200'>2020-07-18</span></td><td><a href='/guix/commit/.guix-authorizations?id=ba1d9680d61d3b06d9b81a81863448f494d654a7'>.guix-authorizations: Add brettgilio (back) to the committers.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-07-01 12:50:22 +0200'>2020-07-01</span></td><td><a href='/guix/commit/.guix-authorizations?id=9f5f3932debc72a57a830fc6ca5ab980f6db4941'>.guix-authorizations: Remove keys of two former contributors.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
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<tr><td><span title='2020-07-01 12:50:22 +0200'>2020-07-01</span></td><td><a href='/guix/commit/.guix-authorizations?id=eb8a79218d33a513d4673162fd752efb1152a084'>.guix-authorizations: Remove brettgilio's old key.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-05-04 10:43:52 +0200'>2020-05-04</span></td><td><a href='/guix/commit/.guix-authorizations?id=d074f73aacc5a39aed0202d6e45721f53f34a8c0'>.guix-authorizations: Add bricewge to the committers.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
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