android: readd 18b ndk

This is referenced in all-packages.nix, so might as well leave it
heref or now.

pkgs/development/androidndk-pkgs/default.nix

@@ -2,6 +2,35 @@
 }:
 
 {
+  "18b" =
+    let
+      ndkVersion = "18.1.5063045";
+
+      buildAndroidComposition = buildPackages.buildPackages.androidenv.composeAndroidPackages {
+        includeNDK = true;
+        inherit ndkVersion;
+      };
+
+      androidComposition = androidenv.composeAndroidPackages {
+        includeNDK = true;
+        inherit ndkVersion;
+      };
+    in
+    import ./androidndk-pkgs.nix {
+      inherit (buildPackages)
+        makeWrapper;
+      inherit (pkgs)
+        stdenv
+        runCommand wrapBintoolsWith wrapCCWith;
+      # buildPackages.foo rather than buildPackages.buildPackages.foo would work,
+      # but for splicing messing up on infinite recursion for the variants we
+      # *dont't* use. Using this workaround, but also making a test to ensure
+      # these two really are the same.
+      buildAndroidndk = buildAndroidComposition.ndk-bundle;
+      androidndk = androidComposition.ndk-bundle;
+      targetAndroidndkPkgs = targetPackages.androidndkPkgs_18b;
+    };
+
   "21" =
     let
       ndkVersion = "21.0.6113669";