Implement parsing additional interop header directly from .def file (#557)

backend.native/tests/interop/basics/4.kt

@@ -1,8 +1,11 @@
 import cstdio.*
 import kotlinx.cinterop.*
 
+val stdout
+    get() = getStdout()
+
 fun main(args: Array<String>) {
-    printf("%s %s %d %d %d %lld %.1f %.1lf\n",
+    fprintf(stdout, "%s %s %d %d %d %lld %.1f %.1lf\n",
             "a", "b".cstr, (-1).toByte(), 2.toShort(), 3, Long.MAX_VALUE, 0.1.toFloat(), 0.2)
 
     memScoped {

backend.native/tests/interop/basics/cstdio.def

@@ -1 +1,7 @@
-headers = stdio.h
+headers = stdio.h
+
+---
+
+static inline FILE* getStdout() {
+    return stdout;
+}