gnu: dbus-c++: Fix build with GCC 7.

* gnu/packages/patches/dbus-c++-gcc-compat.patch,
gnu/packages/patches/dbus-c++-threading-mutex.patch: New files.
* gnu/local.mk (dist_patch_DATA): Adjust accordingly.
* gnu/packages/glib.scm (dbus-c++)[source](patches): New field.
[arguments]: End phases on #t.

gnu/local.mk

@@ -750,6 +750,8 @@ dist_patch_DATA =						\
   %D%/packages/patches/cvs-CVE-2017-12836.patch		\
   %D%/packages/patches/darkice-workaround-fpermissive-error.patch	\
   %D%/packages/patches/dbus-helper-search-path.patch		\
+  %D%/packages/patches/dbus-c++-gcc-compat.patch		\
+  %D%/packages/patches/dbus-c++-threading-mutex.patch		\
   %D%/packages/patches/dealii-mpi-deprecations.patch		\
   %D%/packages/patches/deja-dup-use-ref-keyword-for-iter.patch	\
   %D%/packages/patches/dfu-programmer-fix-libusb.patch		\

gnu/packages/glib.scm

@@ -791,6 +791,8 @@ This package provides the library for GLib applications.")
                 "mirror://sourceforge/dbus-cplusplus/dbus-c%2B%2B/"
                 version "/libdbus-c%2B%2B-" version ".tar.gz"))
               (file-name (string-append name "-" version ".tar.gz"))
+              (patches (search-patches "dbus-c++-gcc-compat.patch"
+                                       "dbus-c++-threading-mutex.patch"))
               (sha256
                (base32
                 "0qafmy2i6dzx4n1dqp6pygyy6gjljnb7hwjcj2z11c1wgclsq4dw"))))
@@ -812,7 +814,8 @@ This package provides the library for GLib applications.")
            (lambda _
              (substitute* "include/dbus-c++/eventloop-integration.h"
                (("#include <errno.h>")
-                "#include <errno.h>\n#include <unistd.h>")))))))
+                "#include <errno.h>\n#include <unistd.h>"))
+             #t)))))
     (synopsis "D-Bus API for C++")
     (description "This package provides D-Bus client API bindings for the C++
 programming language.  It also contains the utility

gnu/packages/patches/dbus-c++-gcc-compat.patch

@@ -0,0 +1,14 @@
+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);
+ }

gnu/packages/patches/dbus-c++-threading-mutex.patch

@@ -0,0 +1,37 @@
+Description: Fix FTBFS if DBUS_HAS_RECURSIVE_MUTEX is undefined
+Author: Peter Williams <peter@newton.cx>
+Last-Update: 2018-01-26
+
+Taken from Debian:
+https://sources.debian.org/src/dbus-c++/0.9.0-8.1/debian/patches/07_fix_mutex_ftbfs.patch/
+
+--- dbus-c++-0.9.0.orig/include/dbus-c++/dispatcher.h
++++ dbus-c++-0.9.0/include/dbus-c++/dispatcher.h
+@@ -267,6 +267,19 @@ struct Threading
+     return new Mx;
+   }
+ 
++#ifndef DBUS_HAS_RECURSIVE_MUTEX
++  static bool mutex_free(Mutex *mx)
++  {
++    delete mx;
++    return true;
++  }
++
++  static bool mutex_lock(Mutex *mx)
++  {
++    mx->lock();
++    return true;
++  }
++#else
+   static void mutex_free(Mutex *mx)
+   {
+     delete mx;
+@@ -276,6 +289,7 @@ struct Threading
+   {
+     mx->lock();
+   }
++#endif
+ 
+   static void mutex_unlock(Mutex *mx)
+   {