gnu: ganv, pavucontrol, jalv: Fix build by compile with C++11.

* gnu/packages/audio.scm (jalv)[arguments],
  gnu/packages/gtk.scm (ganv)[arguments],
  gnu/packages/music.scm (non-sequencer)[arguments],
  gnu/packages/pulseaudio.scm (pavucontrol)[arguments]: Set
  'CXXFLAGS' to '-std=c++11'.

gnu/packages/audio.scm

@@ -746,7 +746,16 @@ (define-public jalv
                (base32
                 "1f1hcq74n3ziw8bk97mn5a1vgw028dxikv3fchaxd430pbbhqgl9"))))
     (build-system waf-build-system)
-    (arguments `(#:tests? #f)) ; no check target
+    (arguments
+     `(#:tests? #f ; no check target
+       #:phases
+       (modify-phases %standard-phases
+         (add-before
+          'configure 'set-flags
+          (lambda _
+            ;; Compile with C++11, required by gtkmm.
+            (setenv "CXXFLAGS" "-std=c++11")
+            #t)))))
     (inputs
      `(("lv2" ,lv2)
        ("lilv" ,lilv)

gnu/packages/gtk.scm

@@ -253,8 +253,10 @@ (define-public ganv
     (build-system waf-build-system)
     (arguments
      `(#:phases (alist-cons-before
-                 'configure 'set-ldflags
+                 'configure 'set-flags
                  (lambda* (#:key outputs #:allow-other-keys)
+                   ;; Compile with C++11, required by gtkmm.
+                   (setenv "CXXFLAGS" "-std=c++11")
                    ;; Allow 'bin/ganv_bench' to find libganv-1.so.
                    (setenv "LDFLAGS"
                            (string-append "-Wl,-rpath="

gnu/packages/music.scm

@@ -346,6 +346,14 @@ (define-public non-sequencer
                                                        (%current-system))))
                      '("--disable-sse")
                      '()))
+         #:phases
+         (modify-phases %standard-phases
+           (add-before
+            'configure 'set-flags
+            (lambda _
+              ;; Compile with C++11, required by libsigc++.
+              (setenv "CXXFLAGS" "-std=c++11")
+              #t)))
          #:python ,python-2))
       (inputs
        `(("jack" ,jack-1)

gnu/packages/pulseaudio.scm

@@ -199,6 +199,8 @@ (define-public pavucontrol
               (base32
                "14486c6lmmirkhscbfygz114f6yzf97h35n3h3pdr27w4mdfmlmk"))))
     (build-system gnu-build-system)
+    (arguments
+     '(#:configure-flags '("CXXFLAGS=-std=c++11"))) ; required by gtkmm
     (inputs
      `(("libcanberra" ,libcanberra)
        ("gtkmm" ,gtkmm)