LibC: Pass the environment as third argument to main()

After some very confused debugging, I discovered that GNU make has a
main() function with this signature:

    int main(int argc, char** argv, char** envp)

Apparently this is a non-standard but widely supported thing, so let's
do the same in Serenity so make works as expected.

This fixes an issue where you had to do "make PATH=..." instead of make
just picking up PATH from the environment. :^)

Libraries/LibC/crt0.cpp

@@ -4,7 +4,7 @@
 
 extern "C" {
 
-int main(int, char**);
+int main(int, char**, char**);
 
 __thread int errno;
 char** environ;
@@ -36,7 +36,7 @@ int _start(int argc, char** argv, char** env)
     for (size_t i = 0; i < size; i++)
         (*__init_array_start[i])(argc, argv, env);
 
-    int status = main(argc, argv);
+    int status = main(argc, argv, environ);
 
     exit(status);