platform.zlib: fix + mingw + test (#1880)

backend.native/tests/interop/platform_zlib.kt

@@ -0,0 +1,21 @@
+import kotlinx.cinterop.*
+import platform.zlib.*
+
+val source = immutableBinaryBlobOf(0xF3, 0x48, 0xCD, 0xC9, 0xC9, 0x57, 0x04, 0x00).asCPointer(0)!!
+val golden = immutableBinaryBlobOf(0x48, 0x65, 0x6C, 0x6C, 0x6F, 0x21, 0x00).asCPointer(0)!!
+
+fun main(args: Array<String>) = memScoped {
+    val buffer = allocArray<ByteVar>(32)
+
+    val z = alloc<z_stream>().apply {
+        next_in   = source
+        avail_in  = 8
+        next_out  = buffer
+        avail_out = 32
+    }.ptr
+
+    if (inflateInit2(z, -15) == Z_OK && inflate(z, Z_FINISH) == Z_STREAM_END && inflateEnd(z) == Z_OK) 
+        println(buffer.toKString())
+
+    println(golden.toKString())
+}