swift: Workaround Hydra darwin build problem

When the host platform is darwin, building swift on Hydra and Github Actions
with ninja 1.12 will both give the same error:

```
ld: warning: directory not found for option '-L/nix/store/g9rbp9m6vs1xj4jl6b6vjb6bm8kgr107-SDKs/MacOSX10.15.sdk/usr/lib/swift'
...
ld: warning: Could not find or use auto-linked library 'swiftCompatibility56'
Undefined symbols for architecture arm64:
  "__swift_FORCE_LOAD_$_swiftCompatibility56", referenced from:
      __swift_FORCE_LOAD_$_swiftCompatibility56_$_Optimizer in libswiftCompilerModules-bootstrapping1.a(Optimizer.o)
  ...
```

Beware the failure does not happen on developers' local machines.

Until we find out the exact cause, pin ninja to version 1.11 to workaround the problem.

pkgs/development/compilers/swift/compiler/default.nix

@@ -190,6 +190,24 @@ let
     '';
   };
 
+  ninja' =
+    if stdenv.hostPlatform.isDarwin then
+      # https://github.com/NixOS/nixpkgs/issues/327836
+      # Fail to build with ninja 1.12 on Hydra when host platform is darwin, but
+      # not on developers' local machines.
+      # Until we find out the exact cause, pin ninja to version 1.11 to
+      # workaround the problem.
+      ninja.overrideAttrs (old: rec {
+        version = "1.11.1";
+        src = old.src.override {
+          rev = version;
+          hash = "sha256-LvV/Fi2ARXBkfyA1paCRmLUwCh/rTyz+tGMg2/qEepI=";
+        };
+        patches = [ ];
+      })
+    else
+      ninja;
+
 in stdenv.mkDerivation {
   pname = "swift";
   inherit (sources) version;
@@ -199,7 +217,7 @@ in stdenv.mkDerivation {
   nativeBuildInputs = [
     cmake
     git
-    ninja
+    ninja'
     perl # pod2man
     pkg-config
     python3