Handle variadic block types in cinterop

#KT-36766 Fixed

Interop/Indexer/src/main/kotlin/org/jetbrains/kotlin/native/interop/indexer/Indexer.kt

@@ -688,7 +688,7 @@ internal class NativeIndexImpl(val library: NativeLibrary, val verbose: Boolean
 
     private fun convertFunctionType(type: CValue<CXType>): Type {
         val kind = type.kind
-        assert(kind == CXType_Unexposed || kind == CXType_FunctionProto)
+        assert(kind == CXType_Unexposed || kind == CXType_FunctionProto || kind == CXType_FunctionNoProto) { kind }
 
         if (clang_isFunctionTypeVariadic(type) != 0) {
             return VoidType // make this function pointer opaque.

backend.native/tests/interop/objc/tests/kt36766.h

@@ -0,0 +1 @@
+void kt36766(void (^block)()) {}

backend.native/tests/interop/objc/tests/kt36766.kt

@@ -0,0 +1,6 @@
+import kotlin.test.*
+import objcTests.*
+
+@Test fun testKt36766() {
+    kt36766(null)
+}