[RFA] Fix leaks by clearing registers and frame caches.

[Philippe Waroquiers]

Valgrind reports leaks such as the below in the tests:
gdb.threads/corethreads.exp
gdb.threads/gcore-thread.exp
gdb.ada/task_switch_in_core.exp
gdb.trace/tfile.exp
gdb.base/siginfo-thread.exp

==12701== 1,123 (72 direct, 1,051 indirect) bytes in 1 blocks are definitely lost in loss record 2,928 of 3,247
==12701==    at 0x4C2C4CC: operator new(unsigned long) (vg_replace_malloc.c:344)
==12701==    by 0x5CF771: get_thread_arch_aspace_regcache(ptid_t, gdbarch*, address_space*) (regcache.c:330)
==12701==    by 0x5CF92A: get_thread_regcache (regcache.c:366)
==12701==    by 0x5CF92A: get_current_regcache() (regcache.c:372)
==12701==    by 0x4C7964: get_current_frame() (frame.c:1587)
==12701==    by 0x4C7A3C: get_selected_frame(char const*) (frame.c:1651)
==12701==    by 0x669EAD: print_thread_info_1(ui_out*, char const*, int, int, int) (thread.c:1151)
==12701==    by 0x66A9A1: info_threads_command(char const*, int) (thread.c:1217)
==12701==    by 0x40A878: cmd_func(cmd_list_element*, char const*, int) (cli-decode.c:1892)
...

Fix these leaks by clearing registers and frame caches.
This leak and fix is similar to the leak fixed by 799efbe8e01
---
 gdb/ChangeLog  | 5 +++++
 gdb/corelow.c  | 2 ++
 gdb/inferior.c | 4 ++++
 3 files changed, 11 insertions(+)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index eba0426463..ce18121a13 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -6229,3 +6229,8 @@ version-control: never
 coding: utf-8
 End:
 
+2019-04-01  Philippe Waroquiers  <philippe.waroquiers@skynet.be>
+
+	* corelow.c (core_target::detach): Ensure frame cache and
+	register caches are cleared.
+	inferior.c (exit_inferior_1): Likewise.
diff --git a/gdb/corelow.c b/gdb/corelow.c
index 3ce612d31b..9fcc2d2372 100644
--- a/gdb/corelow.c
+++ b/gdb/corelow.c
@@ -535,6 +535,8 @@ core_target::detach (inferior *inf, int from_tty)
      'this'.  */
   unpush_target (this);
 
+  /* Clear the register cache and the frame cache.  */
+  registers_changed ();
   reinit_frame_cache ();
   maybe_say_no_core_file_now (from_tty);
 }
diff --git a/gdb/inferior.c b/gdb/inferior.c
index e7b49376e9..abfef700c3 100644
--- a/gdb/inferior.c
+++ b/gdb/inferior.c
@@ -208,6 +208,10 @@ exit_inferior_1 (struct inferior *inftoex, int silent)
   inf->pending_detach = 0;
   /* Reset it.  */
   inf->control = inferior_control_state (NO_STOP_QUIETLY);
+
+  /* Clear the register cache and the frame cache.  */
+  registers_changed ();
+  reinit_frame_cache ();
 }
 
 void
-- 
2.20.1