Revert "[wasm] Fix ambiguous errno error when importing WASILibc module"

This reverts commit 164ec0a.

Author: kateinoigakukun

stdlib/public/Platform/Platform.swift

@@ -84,11 +84,6 @@ func _convertDarwinBooleanToBool(_ x: DarwinBoolean) -> Bool {
 
 #endif
 
-// wasi-libc defines `errno` in a way ClangImporter can understand, so we don't
-// need to define shims for it. On the contrary, if we define the shim, we will
-// get an ambiguity error when importing WASILibc module and SwiftWASILibc Clang
-// module (or a Clang module that re-exports SwiftWASILibc).
-#if !os(WASI)
 //===----------------------------------------------------------------------===//
 // sys/errno.h
 //===----------------------------------------------------------------------===//
@@ -101,7 +96,6 @@ public var errno : Int32 {
     return _swift_stdlib_setErrno(val)
   }
 }
-#endif
 
 
 //===----------------------------------------------------------------------===//