Use the existing _stdlib_atomic*ARCRef methods

Didn't realize these methods existed; no need for shims or wrappers!

Author: natecook1000

Package.swift

@@ -60,18 +60,11 @@ let package = Package(
         .target(
             name: "_CUnicode",
             dependencies: []),
-        .target(
-            name: "_LazyAtomicShims",
-            dependencies: []),
-        .target(
-            name: "_LazyAtomic",
-            dependencies: ["_LazyAtomicShims"]),
         .target(
             name: "_StringProcessing",
             dependencies: [
               "_RegexParser",
               "_CUnicode",
-              "_LazyAtomic",
             ],
             swiftSettings: publicStdlibSettings),
         .target(