palemoon: use gcc7, remove build notification

Changes as requested in https://github.com/NixOS/nixpkgs/pull/69206

pkgs/applications/networking/browsers/palemoon/default.nix

@@ -55,6 +55,7 @@ in stdenv.mkDerivation rec {
   configurePhase = ''
     export MOZBUILD_STATE_PATH=$(pwd)/mozbuild
     export MOZCONFIG=$(pwd)/mozconfig
+    export MOZ_NOSPAM=1
     export builddir=$(pwd)/pmbuild
 
     echo > $MOZCONFIG "

pkgs/top-level/all-packages.nix

@@ -20621,8 +20621,8 @@ in
   osmo = callPackage ../applications/office/osmo { };
 
   palemoon = callPackage ../applications/networking/browsers/palemoon {
-    # https://forum.palemoon.org/viewtopic.php?f=57&t=15296#p111146
-    stdenv = gcc49Stdenv;
+    # https://www.palemoon.org/sourcecode.shtml
+    stdenv = gcc7Stdenv;
   };
 
   pamix = callPackage ../applications/audio/pamix { };