LibC: Move C++ABI functions to cxxabi.cpp, typecheck cxa_atexit

Author: https://github.com/BenWiederhake
Commit: ff590db7e5
Pull-request: https://github.com/SerenityOS/serenity/pull/3096
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/stelar7

Libraries/LibC/stdlib.cpp

@@ -40,6 +40,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/internals.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
 #include <sys/wait.h>
@@ -197,10 +198,6 @@ __attribute__((warn_unused_result)) int __generate_unique_filename(char* pattern
 
 extern "C" {
 
-// Itanium C++ ABI methods defined in crt0.cpp
-extern int __cxa_atexit(void (*function)(void*), void* paramter, void* dso_handle);
-extern void __cxa_finalize(void* dso_handle);
-
 void exit(int status)
 {
     __cxa_finalize(nullptr);