Merge commit staging+systemd into closure-size

Many non-conflict problems weren't (fully) resolved in this commit yet.

pkgs/development/libraries/gmp/5.1.x.nix

@@ -1,6 +1,6 @@
 { stdenv, fetchurl, m4, cxx ? true, withStatic ? true }:
 
-with { inherit (stdenv.lib) optional; };
+with { inherit (stdenv.lib) optional optionalString; };
 
 stdenv.mkDerivation rec {
   name = "gmp-5.1.3";
@@ -30,6 +30,13 @@ stdenv.mkDerivation rec {
     ++ optional stdenv.is64bit "--with-pic"
     ;
 
+  # The config.guess in GMP tries to runtime-detect various
+  # ARM optimization flags via /proc/cpuinfo (and is also
+  # broken on multicore CPUs). Avoid this impurity.
+  preConfigure = optionalString stdenv.isArm ''
+      configureFlagsArray+=("--build=$(./configfsf.guess)")
+    '';
+
   doCheck = true;
 
   dontDisableStatic = withStatic;