cmake: bring back 3.9 for Darwin bootstrap

Broken by ba6e0ae33df36; see e.g. https://hydra.nixos.org/build/68223628

pkgs/development/tools/build-managers/cmake/default.nix

···
 { stdenv, fetchurl, pkgconfig
 , bzip2, curl, expat, libarchive, xz, zlib, libuv, rhash
+, majorVersion ? "3.10"
 # darwin attributes
 , ps
 , isBootstrap ? false
···
 
 with stdenv.lib;
 
+with (
+  {
+    "3.10" = {
+      minorVersion = "2";
+      sha256 = "80d0faad4ab56de07aa21a7fc692c88c4ce6156d42b0579c6962004a70a3218b";
+    };
+    "3.9" = {
+      minorVersion = "6";
+      sha256 = "7410851a783a41b521214ad987bb534a7e4a65e059651a2514e6ebfc8f46b218";
+    };
+
+  }.${majorVersion}
+    or (abort ''Unsupported configuration for cmake: majorVersion = "${majorVersion}";'')
+);
+
 let
   os = stdenv.lib.optionalString;
-  majorVersion = "3.10";
-  minorVersion = "2";
   version = "${majorVersion}.${minorVersion}";
 in
 
···
   src = fetchurl {
     url = "${meta.homepage}files/v${majorVersion}/cmake-${version}.tar.gz";
     # from https://cmake.org/files/v3.10/cmake-3.10.2-SHA-256.txt
-    sha256 = "80d0faad4ab56de07aa21a7fc692c88c4ce6156d42b0579c6962004a70a3218b";
+    inherit sha256;
   };
 
   prePatch = optionalString (!useSharedLibraries) ''

pkgs/top-level/all-packages.nix

···
   llvmPackages_4 = callPackage ../development/compilers/llvm/4 ({
     inherit (stdenvAdapters) overrideCC;
   } // stdenv.lib.optionalAttrs stdenv.isDarwin {
-    cmake = cmake.override { isBootstrap = true; };
+    cmake = cmake.override {
+      isBootstrap = true;
+      majorVersion = "3.9"; # 3.10.2: 'ApplicationServices/ApplicationServices.h' file not found
+    };
     libxml2 = libxml2.override { pythonSupport = false; };
     python2 = callPackage ../development/interpreters/python/cpython/2.7/boot.nix { inherit (darwin) CF configd; };
   });