[wasm] Gate atomic write option usages behind platform check

`Data.WritingOptions.atomic` is now unavailable on WASI: swiftlang/swift-foundation#992

Author: kateinoigakukun

Sources/Foundation/NSData.swift

@@ -433,10 +433,12 @@ open class NSData : NSObject, NSCopying, NSMutableCopying, NSSecureCoding {
 #if os(WASI)
         // WASI does not have permission concept
         let permissions: Int? = nil
+        var atomicWrite: Bool { false }
 #else
         let permissions = try? fm.attributesOfItem(atPath: path)[.posixPermissions] as? Int
+        let atomicWrite = writeOptionsMask.contains(.atomic)
 #endif
-        if writeOptionsMask.contains(.atomic) {
+        if atomicWrite {
             let (newFD, auxFilePath) = try _NSCreateTemporaryFile(path)
             let fh = FileHandle(fileDescriptor: newFD, closeOnDealloc: true)
             do {
@@ -489,7 +491,12 @@ open class NSData : NSObject, NSCopying, NSMutableCopying, NSSecureCoding {
     /// NOTE: the 'atomically' flag is ignored if the url is not of a type the supports atomic writes
     open func write(toFile path: String, atomically useAuxiliaryFile: Bool) -> Bool {
         do {
-            try write(toFile: path, options: useAuxiliaryFile ? .atomic : [])
+            #if os(WASI)
+            let options: WritingOptions = []
+            #else
+            let options: WritingOptions = useAuxiliaryFile ? .atomic : []
+            #endif
+            try write(toFile: path, options: options)
         } catch {
             return false
         }

Sources/Foundation/NSString.swift

@@ -1261,7 +1261,12 @@ extension NSString {
     internal func _writeTo(_ url: URL, _ useAuxiliaryFile: Bool, _ enc: UInt) throws {
         var data = Data()
         try _getExternalRepresentation(&data, url, enc)
-        try data.write(to: url, options: useAuxiliaryFile ? .atomic : [])
+        #if os(WASI)
+        let options: Data.WritingOptions = []
+        #else
+        let options: Data.WritingOptions = useAuxiliaryFile ? .atomic : []
+        #endif
+        try data.write(to: url, options: options)
     }
 
     public func write(to url: URL, atomically useAuxiliaryFile: Bool, encoding enc: UInt) throws {