treewide: Start to break up static overlay

We can use use `stdenv.hostPlatform.isStatic` instead, and move the
logic per package. The least opionated benefit of this is that it makes
it much easier to replace packages with modified ones, as there is no
longer any issue of overlay order.

CC @FRidh @matthewbauer

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

@@ -1,4 +1,7 @@
-{ stdenv, fetchurl, m4, cxx ? true, withStatic ? true }:
+{ stdenv, fetchurl, m4
+, cxx ? true
+, withStatic ? stdenv.hostPlatform.isStatic
+}:
 
 let inherit (stdenv.lib) optional; in
 

pkgs/development/libraries/gmp/6.x.nix

@@ -1,7 +1,8 @@
 { stdenv, fetchurl, m4
 , cxx ? !stdenv.hostPlatform.useAndroidPrebuilt && !stdenv.hostPlatform.isWasm
 , buildPackages
-, withStatic ? false }:
+, withStatic ? stdenv.hostPlatform.isStatic
+}:
 
 # Note: this package is used for bootstrapping fetchurl, and thus
 # cannot use fetchpatch! All mutable patches (generated by GitHub or