Fix an incorrect comment on spawn_func

spawn_func calls pthread_create on unix, not fork

Fix on existing code split out of compat.c into
compat_pthreads.c in c2f0d52b

changes/bug16115-spawn-comment

+  o Minor fixes (threads, comments):
+    - Fix an incorrect comment on spawn_func in compat_pthreads.c.
+      spawn_func calls pthread_create on unix, not fork
+      Patch by "teor".
+      Bugfix on unknown tor version (existing code split out of
+      compat.c into compat_pthreads.c in c2f0d52b7fb9 on 22 Sep 2013).

src/common/compat_pthreads.c

@@ -50,7 +50,8 @@ static pthread_attr_t attr_detached;
 static int threads_initialized = 0;
 
 /** Minimalist interface to run a void function in the background.  On
- * Unix calls fork, on win32 calls beginthread.  Returns -1 on failure.
+ * Unix calls pthread_create, on win32 calls beginthread.  Returns -1 on
+ * failure.
  * func should not return, but rather should call spawn_exit.
  *
  * NOTE: if <b>data</b> is used, it should not be allocated on the stack,