Added minimal posix.def for windows.

backend.native/tests/build.gradle

@@ -1236,7 +1236,8 @@ task link_omit_unused(type: LinkKonanTest) {
 }
 
 task link_default_libs(type: RunKonanTest) {
-    goldValue = "ptrdiff = 0\n"
+    disabled = (project.testTarget == 'wasm32') // there will be no posix.klib for wasm
+    goldValue = "sizet = 0\n"
     source = "link/default/default.kt"
 }
 

backend.native/tests/link/default/default.kt

@@ -2,6 +2,6 @@ import posix.*
 
 fun main(args: Array<String>) {
     // Just check the typealias is in scope.
-    val ptrdiff: ptrdiff_t = 0L
-    println("ptrdiff = $ptrdiff")
+    val sizet: size_t = 0L
+    println("sizet = $sizet")
 }

klib/src/platform/windows/posix.def

@@ -0,0 +1,3 @@
+package = platform.posix
+headers = stdio.h
+compilerOpts = -DUNICODE -Wno-incompatible-pointer-types -Wno-deprecated-declarations