Merge commit '18aa59b0f26fc707e7313f8467e67159e61600c2' from master into staging

There was one conflict in the NixOS manual; I checked that it still
built after resolving it.

pkgs/development/compilers/gcc/8/default.nix

@@ -322,6 +322,13 @@ stdenv.mkDerivation ({
 
   LIBRARY_PATH = optionals (targetPlatform == hostPlatform) (makeLibraryPath (optional (zlib != null) zlib));
 
+  EXTRA_TARGET_FLAGS = optionals
+    (targetPlatform != hostPlatform && libcCross != null)
+    ([
+      "-idirafter ${getDev libcCross}${libcCross.incdir or "/include"}"
+    ] ++ optionals (! crossStageStatic) [
+      "-B${libcCross.out}${libcCross.libdir or "/lib"}"
+    ]);
 
   EXTRA_TARGET_LDFLAGS = optionals
     (targetPlatform != hostPlatform && libcCross != null)