sourcery: statically link Swift runtime libraries

The current formula _requires_ that the user have the exact same version
of Xcode as Homebrew's Jenkins CI machines located exactly at the same
location (`/Applications/Xcode.app`).

That's because the formula uses Swift Package Manager to build the
bottle, which adds an `LC_RPATH` command to the binary with an absolute
path to the SDK where the Swift runtime dynamic libraries can be found.

So if you've installed Xcode anywhere else, or if the version of Xcode
you have installed at that location isn't the same version as was used
on Homebrew's Jenkins machines, you'll have to build from source using a
command like `brew install sourcery --HEAD`.

Formula/sourcery.rb

@@ -3,6 +3,7 @@ class Sourcery < Formula
   homepage "https://github.com/krzysztofzablocki/Sourcery"
   url "https://github.com/krzysztofzablocki/Sourcery/archive/0.5.9.tar.gz"
   sha256 "1f5dee5184a7271a70552c0e85dd1d730e711088e5fdcf3dd7aa1f96b993e414"
+  revision 1
 
   bottle do
     cellar :any
@@ -15,7 +16,7 @@ class Sourcery < Formula
   def install
     ENV.delete("CC")
     ENV["SDKROOT"] = MacOS.sdk_path
-    system "swift", "build", "-c", "release"
+    system "swift", "build", "-c", "release", "-Xswiftc", "-static-stdlib"
     bin.install ".build/release/sourcery"
     lib.install Dir[".build/release/*.dylib"]
   end