Implement varargs in interop for Kotlin N (#393)

* Implement CValues.equals and .hashCode

* Add trivial test for interop varargs

* Implement varargs in interop for Kotlin N

* Compile and link runtime with libffi

* Fix few places.

runtime/build.gradle

@@ -11,6 +11,7 @@ targetList.each { targetName ->
         target targetName
         compilerArgs targetArgs[targetName]
         compilerArgs '-I' + project.file('../common/src/hash/headers')
+        compilerArgs '-I' + project.file(rootProject.ext.get("${targetName}LibffiDir") + "/include")
         linkerArgs project.file("../common/build/$targetName/hash.bc").path
     }
 }

runtime/src/main/cpp/Interop.cpp

@@ -0,0 +1,57 @@
+#include <assert.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <ffi.h>
+
+namespace {
+
+typedef int FfiTypeKind;
+// Also declared in Varargs.kt
+const FfiTypeKind FFI_TYPE_KIND_VOID = 0;
+const FfiTypeKind FFI_TYPE_KIND_SINT8 = 1;
+const FfiTypeKind FFI_TYPE_KIND_SINT16 = 2;
+const FfiTypeKind FFI_TYPE_KIND_SINT32 = 3;
+const FfiTypeKind FFI_TYPE_KIND_SINT64 = 4;
+const FfiTypeKind FFI_TYPE_KIND_FLOAT = 5;
+const FfiTypeKind FFI_TYPE_KIND_DOUBLE = 6;
+const FfiTypeKind FFI_TYPE_KIND_POINTER = 7;
+
+ffi_type* convertFfiTypeKindToType(FfiTypeKind typeKind) {
+    switch (typeKind) {
+        case FFI_TYPE_KIND_VOID: return &ffi_type_void;
+        case FFI_TYPE_KIND_SINT8: return &ffi_type_sint8;
+        case FFI_TYPE_KIND_SINT16: return &ffi_type_sint16;
+        case FFI_TYPE_KIND_SINT32: return &ffi_type_sint32;
+        case FFI_TYPE_KIND_SINT64: return &ffi_type_sint64;
+        case FFI_TYPE_KIND_FLOAT: return &ffi_type_float;
+        case FFI_TYPE_KIND_DOUBLE: return &ffi_type_double;
+        case FFI_TYPE_KIND_POINTER: return &ffi_type_pointer;
+
+        default: assert(false);
+    }
+}
+
+}  // namespace
+
+extern "C" {
+
+void callWithVarargs(void* codePtr, void* returnValuePtr, FfiTypeKind returnTypeKind,
+                     void** arguments, intptr_t* argumentTypeKinds,
+                     int fixedArgumentsNumber, int totalArgumentsNumber) {
+
+
+    ffi_type** argumentTypes = (ffi_type**)argumentTypeKinds;
+    // In-place convertion:
+    for (int i = 0; i < totalArgumentsNumber; ++i) {
+        argumentTypes[i] = convertFfiTypeKindToType((FfiTypeKind) argumentTypeKinds[i]);
+    }
+
+    ffi_cif cif;
+    ffi_prep_cif_var(&cif, FFI_DEFAULT_ABI,
+                     fixedArgumentsNumber, totalArgumentsNumber,
+                     convertFfiTypeKindToType(returnTypeKind), argumentTypes);
+
+    ffi_call(&cif, (void (*)())codePtr, returnValuePtr, arguments);
+}
+
+}