Tweak "Using the running image of ..." output

Currently, "info files" and "info program" on a few native targets
show:

 (gdb) info files
 Symbols from "/home/pedro/gdb/tests/threads".
 Native process:
	 Using the running image of child Thread 0x7ffff7d89740 (LWP 1097968).
					  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 ...

 (gdb) info program
	 Using the running image of child Thread 0x7ffff7d89740 (LWP 1097968).
					  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 Program stopped at 0x555555555278.
 ...


This patch changes them to:

 (gdb) info files
 Symbols from "/home/pedro/gdb/tests/threads".
 Native process:
	 Using the running image of child process 1097968.
	                                  ^^^^^^^^^^^^^^^
 ...

 (gdb) info program
	 Using the running image of child process 1097968.
	                                  ^^^^^^^^^^^^^^^
 Program stopped at 0x555555555278.
 ...


... which I think makes a lot more sense in this context.  The "info
program" manual entry even says:

  "Display information about the status of your program: whether it is
   running or not, what process it is, and why it stopped."
                        ^^^^^^^^^^^^^

This change affects ptrace targets, procfs targets, and Windows.

Approved-By: Simon Marchi <simon.marchi@efficios.com>
Change-Id: I6aab061ff494a84ba3398cf98fd49efd7a6ec1ca