Merge pull request #1523 from kateinoigakukun/yt/wasm-llvm-tools

Prefer `llvm-ar` over `ar` on WebAssembly

Author: kateinoigakukun

Sources/SwiftDriver/Toolchains/WebAssemblyToolchain.swift

@@ -95,10 +95,7 @@ public final class WebAssemblyToolchain: Toolchain {
     switch tool {
     case .swiftCompiler:
       return try lookup(executable: "swift-frontend")
-    case .staticLinker(nil):
-      return try lookup(executable: "ar")
-    case .staticLinker(.llvmFull),
-         .staticLinker(.llvmThin):
+    case .staticLinker:
       return try lookup(executable: "llvm-ar")
     case .dynamicLinker:
       // FIXME: This needs to look in the tools_directory first.