run-command.h: include thread-utils.h instead of pthread.h

run-command.c may use threads for its async support. But instead of
including pthread.h directly, let's include thread-utils.h.

run-command.c probably never needs the dummy bits in thread-utils.h
when NO_PTHREADS is defined. But this makes sure we have consistent
HAVE_THREADS behavior everywhere. From now on outside compat/,
thread-utils.h is the only place that includes pthread.h

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

run-command.h

@@ -1,9 +1,7 @@
 #ifndef RUN_COMMAND_H
 #define RUN_COMMAND_H
 
-#ifndef NO_PTHREADS
-#include <pthread.h>
-#endif
+#include "thread-utils.h"
 
 #include "argv-array.h"