Get rid of SERENITY macro since the compiler already defines __serenity__

This makes it a bit easier to use AK templates out-of-tree.

AK/Assertions.h

@@ -3,7 +3,11 @@
 #ifdef KERNEL
 #include <Kernel/Assertions.h>
 #else
-#include <LibC/assert.h>
+#include <assert.h>
+#ifndef __serenity__
+#define ASSERT assert
+#define ASSERT_NOT_REACHED assert(false)
+#endif
 #endif
 
 namespace AK {

AK/StdLibExtras.h

@@ -3,8 +3,8 @@
 #ifdef KERNEL
 #include <Kernel/StdLib.h>
 #else
-#include <LibC/stdlib.h>
-#include <LibC/string.h>
+#include <stdlib.h>
+#include <string.h>
 #endif
 
 #define UNUSED_PARAM(x) (void)x

AK/Types.h

@@ -1,6 +1,6 @@
 #pragma once
 
-#if defined(SERENITY)
+#ifdef __serenity__
 typedef unsigned char byte;
 typedef unsigned short word;
 typedef unsigned int dword;

AK/kmalloc.cpp

@@ -1,34 +1,11 @@
 #include "kmalloc.h"
 
-#ifndef SERENITY
+#ifndef __serenity__
 #include <cstdlib>
 #endif
 
 extern "C" {
 
-void* kcalloc(size_t nmemb, size_t size)
-{
-    return calloc(nmemb, size);
-}
 
-void* kmalloc(size_t size)
-{
-    return malloc(size);
-}
-
-void kfree(void* ptr)
-{
-    free(ptr);
-}
-
-void* krealloc(void* ptr, size_t size)
-{
-    return realloc(ptr, size);
-}
-
-void* kmalloc_eternal(size_t size)
-{
-    return kmalloc(size);
-}
 
 }

AK/kmalloc.h

@@ -1,6 +1,6 @@
 #pragma once
 
-#if defined(SERENITY) && defined(KERNEL)
+#ifdef KERNEL
 #define AK_MAKE_ETERNAL \
 public: \
     void* operator new(size_t size) { return kmalloc_eternal(size); } \
@@ -12,17 +12,14 @@ private:
 #ifdef KERNEL
 #include <Kernel/kmalloc.h>
 #else
-#include <LibC/stdlib.h>
+#include <stdlib.h>
 
-extern "C" {
-
-[[gnu::malloc, gnu::returns_nonnull]] void* kmalloc(size_t size);
-[[gnu::malloc, gnu::returns_nonnull]] void* kmalloc_eternal(size_t);
-[[gnu::returns_nonnull]] void* krealloc(void* ptr, size_t size);
-void kfree(void* ptr);
-
-}
+#define kcalloc calloc
+#define kmalloc malloc
+#define kfree free
+#define krealloc realloc
 
+#ifdef __serenity__
 inline void* operator new(size_t size)
 {
     return kmalloc(size);
@@ -47,5 +44,6 @@ inline void* operator new(size_t, void* ptr)
 {
     return ptr;
 }
+#endif
 
 #endif