Update toolchain version and work test on macOS

Author: kateinoigakukun

.github/workflows/test.yml

@@ -8,7 +8,7 @@ jobs:
         os: [macOS-10.15]
         include:
           - os: macOS-10.15
-            toolchain: https://github.com/swiftwasm/swift/releases/download/swift-wasm-DEVELOPMENT-SNAPSHOT-2020-04-27-a/swift-wasm-DEVELOPMENT-SNAPSHOT-2020-04-27-a-osx.tar.gz
+            toolchain: https://github.com/swiftwasm/swift/releases/download/swift-wasm-DEVELOPMENT-SNAPSHOT-2020-05-10-a/swift-wasm-DEVELOPMENT-SNAPSHOT-2020-05-10-a-osx.tar.gz
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout

.swift-version

@@ -1 +1 @@
-wasm-DEVELOPMENT-SNAPSHOT-2020-04-27-a
+wasm-DEVELOPMENT-SNAPSHOT-2020-05-10-a

README.md

@@ -13,9 +13,9 @@ The toolchains can be installed via [`swiftenv`](https://github.com/kylef/swifte
 e.g.
 ```sh
 
-$ swiftenv install https://github.com/swiftwasm/swift/releases/download/swift-wasm-DEVELOPMENT-SNAPSHOT-2020-04-27-a/swift-wasm-DEVELOPMENT-SNAPSHOT-2020-04-27-a-osx.tar.gz
+$ swiftenv install https://github.com/swiftwasm/swift/releases/download/swift-wasm-DEVELOPMENT-SNAPSHOT-2020-05-10-a/swift-wasm-DEVELOPMENT-SNAPSHOT-2020-05-10-a-osx.tar.gz
 $ swift --version
-Swift version 5.3-dev (LLVM 7fc8796bc1, Swift 5be35e7aee)
+Swift version 5.3-dev (LLVM 47c28180d7, Swift 5f96d487e0)
 Target: x86_64-apple-darwin19.3.0
 ```
 

Sources/JavaScriptKit/XcodeSupport.swift

@@ -5,7 +5,7 @@ import _CJavaScriptKit
 /// SwiftPM doesn't support WebAssembly target yet, so we need to define them to
 /// avoid link failure.
 /// When running with JavaScript runtime library, they are ignored completely.
-#if Xcode
+#if !arch(wasm32)
 func _set_prop(
     _ _this: JavaScriptObjectRef,
     _ prop: UnsafePointer<Int8>!, _ length: Int32,