Kernel: Implement a simple process time profiler

The kernel now supports basic profiling of all the threads in a process
by calling profiling_enable(pid_t). You finish the profiling by calling
profiling_disable(pid_t).

This all works by recording thread stacks when the timer interrupt
fires and the current thread is in a process being profiled.
Note that symbolication is deferred until profiling_disable() to avoid
adding more noise than necessary to the profile.

A simple "/bin/profile" command is included here that can be used to
start/stop profiling like so:

    $ profile 10 on
    ... wait ...
    $ profile 10 off

After a profile has been recorded, it can be fetched in /proc/profile

There are various limits (or "bugs") on this mechanism at the moment:

- Only one process can be profiled at a time.
- We allocate 8MB for the samples, if you use more space, things will
  not work, and probably break a bit.
- Things will probably fall apart if the profiled process dies during
  profiling, or while extracing /proc/profile

Kernel/Process.cpp

@@ -28,6 +28,7 @@
 #include <Kernel/Net/Socket.h>
 #include <Kernel/Process.h>
 #include <Kernel/ProcessTracer.h>
+#include <Kernel/Profiling.h>
 #include <Kernel/RTC.h>
 #include <Kernel/Scheduler.h>
 #include <Kernel/SharedBuffer.h>
@@ -3701,3 +3702,29 @@ int Process::sys$module_unload(const char* name, size_t name_length)
     g_modules->remove(it);
     return 0;
 }
+
+int Process::sys$profiling_enable(pid_t pid)
+{
+    InterruptDisabler disabler;
+    auto* process = Process::from_pid(pid);
+    if (!process)
+        return -ESRCH;
+    if (!is_superuser() && process->uid() != m_uid)
+        return -EPERM;
+    Profiling::start(*process);
+    process->set_profiling(true);
+    return 0;
+}
+
+int Process::sys$profiling_disable(pid_t pid)
+{
+    InterruptDisabler disabler;
+    auto* process = Process::from_pid(pid);
+    if (!process)
+        return -ESRCH;
+    if (!is_superuser() && process->uid() != m_uid)
+        return -EPERM;
+    process->set_profiling(false);
+    Profiling::stop();
+    return 0;
+}