SwiftPrivate/IO.swift: unify #if canImport checks on non-Windows platforms (#67142)

This simplifies the import statements and adds support for WASILibc.

Author: MaxDesiatov

stdlib/private/SwiftPrivate/IO.swift

@@ -13,19 +13,21 @@
 import Swift
 import SwiftShims
 
+#if os(Windows)
+import CRT
+import WinSDK
+#else
 #if canImport(Darwin)
 import Darwin
-let (platform_read, platform_write, platform_close) = (read, write, close)
 #elseif canImport(Glibc)
 import Glibc
-let (platform_read, platform_write, platform_close) = (read, write, close)
 #elseif canImport(Musl)
 import Musl
-let (platform_read, platform_write, platform_close) = (read, write, close)
-#elseif os(Windows)
-import CRT
-import WinSDK
+#elseif canImport(WASILibc)
+import WASILibc
 #endif
+let (platform_read, platform_write, platform_close) = (read, write, close)
+#endif 
 
 #if os(Windows)
 public struct _FDInputStream {