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

backend.native/tests/build.gradle

@@ -2841,6 +2841,12 @@ task interop_libiconv(type: RunStandaloneKonanTest) {
     goldValue = "72 72\n101 101\n108 108\n108 108\n111 111\n33 33\n"
 }
 
+task interop_zlib(type: RunStandaloneKonanTest) {
+    disabled = (project.testTarget != null)
+    source = "interop/platform_zlib.kt"
+    goldValue = "Hello!\nHello!\n"
+}
+
 task produce_dynamic(type: DynamicKonanTest) {
     disabled = (project.testTarget != null && project.testTarget != project.hostName)
     source = "produce_dynamic/simple/hello.kt"

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())
+}