Update notes about building for the Swift static linking changes.

Fixes apple#857.

Author: thomasvl

Documentation/PLUGIN.md

@@ -34,13 +34,17 @@ Building the plugin should be simple on any supported Swift platform:
 ```
 $ git clone https://github.com/apple/swift-protobuf
 $ cd swift-protobuf
-$ swift build -c release -Xswiftc -static-stdlib
+$ swift build -c release
 ```
 
 This will create a binary called `protoc-gen-swift` in the
 `.build/release` directory.  To install, just copy this one executable
 anywhere in your PATH.
 
+NOTE: The Swift runtime support is now included with macOS. If you are
+using old Xcode versions or are on older system versions, you might need
+to use also use `--static-swift-stdlib` with `swift build`.
+
 ### Converting .proto files into Swift
 
 To generate Swift output for your .proto files, you run the `protoc`

README.md

@@ -127,14 +127,19 @@ build the protoc plugin:
 
 ```
 $ git checkout tags/[tag_name]
-$ swift build --static-swift-stdlib -c release
+$ swift build -c release
 ```
 
 This will create a binary called `protoc-gen-swift` in the `.build/release`
 directory.
+
 To install, just copy this one executable into a directory that is
 part of your `PATH` environment variable.
 
+NOTE: The Swift runtime support is now included with macOS. If you are
+using old Xcode versions or are on older system versions, you might need
+to use also use `--static-swift-stdlib` with `swift build`.
+
 ### Alternatively install via Homebrew
 
 If you prefer using [Homebrew](https://brew.sh):