Add sys$set_mmap_name and use it from LibC's malloc.

It's nice to be able to identify mmap's in /proc/PID/vm.

Kernel/Syscall.cpp

@@ -114,6 +114,8 @@ DWORD handle(DWORD function, DWORD arg1, DWORD arg2, DWORD arg3)
         return current->sys$chdir((const char*)arg1);
     case Syscall::PosixUname:
         return current->sys$uname((utsname*)arg1);
+    case Syscall::SetMmapName:
+        return current->sys$set_mmap_name((void*)arg1, (size_t)arg2, (const char*)arg3);
     default:
         kprintf("int0x80: Unknown function %x requested {%x, %x, %x}\n", function, arg1, arg2, arg3);
         break;