Rename current_inferior as current_thread in gdbserver

GDB has a function named "current_inferior" and gdbserver has a global
variable named "current_inferior", but the two are not equivalent;
indeed, gdbserver does not have any real equivalent of what GDB calls
an inferior.  What gdbserver's "current_inferior" is actually pointing
to is a structure describing the current thread.  This commit renames
current_inferior as current_thread in gdbserver to clarify this.  It
also renames the function "set_desired_inferior" to "set_desired_thread"
and renames various local variables from foo_inferior to foo_thread.

gdb/gdbserver/ChangeLog:

	* inferiors.h (current_inferior): Renamed as...
	(current_thread): New variable.  All uses updated.
	* linux-low.c (get_pc): Renamed saved_inferior as saved_thread.
	(maybe_move_out_of_jump_pad): Likewise.
	(cancel_breakpoint): Likewise.
	(linux_low_filter_event): Likewise.
	(wait_for_sigstop): Likewise.
	(linux_resume_one_lwp): Likewise.
	(need_step_over_p): Likewise.
	(start_step_over): Likewise.
	(linux_stabilize_threads): Renamed save_inferior as saved_thread.
	* linux-x86-low.c (x86_linux_update_xmltarget): Likewise.
	* proc-service.c (ps_lgetregs): Renamed reg_inferior as reg_thread
	and save_inferior as saved_thread.
	* regcache.c (get_thread_regcache): Renamed saved_inferior as
	saved_thread.
	(regcache_invalidate_thread): Likewise.
	* remote-utils.c (prepare_resume_reply): Likewise.
	* thread-db.c (thread_db_get_tls_address): Likewise.
	(disable_thread_event_reporting): Likewise.
	(remove_thread_event_breakpoints): Likewise.
	* tracepoint.c (gdb_agent_about_to_close): Renamed save_inferior
	as saved_thread.
	* target.h (set_desired_inferior): Renamed as...
	(set_desired_thread): New declaration.  All uses updated.
	* server.c (myresume): Updated comment to reference thread instead
	of inferior.
	(handle_serial_event): Likewise.
	(handle_target_event): Likewise.

gdb/gdbserver/linux-x86-low.c

@@ -231,7 +231,7 @@ static /*const*/ int i386_regmap[] =
 static int
 is_64bit_tdesc (void)
 {
-  struct regcache *regcache = get_thread_regcache (current_inferior, 0);
+  struct regcache *regcache = get_thread_regcache (current_thread, 0);
 
   return register_size (regcache->tdesc, 0) == 8;
 }
@@ -590,7 +590,7 @@ static void
 x86_dr_low_set_addr (int regnum, CORE_ADDR addr)
 {
   /* Only update the threads of this process.  */
-  int pid = pid_of (current_inferior);
+  int pid = pid_of (current_thread);
 
   gdb_assert (DR_FIRSTADDR <= regnum && regnum <= DR_LASTADDR);
 
@@ -602,7 +602,7 @@ x86_dr_low_set_addr (int regnum, CORE_ADDR addr)
 static CORE_ADDR
 x86_dr_low_get_addr (int regnum)
 {
-  ptid_t ptid = ptid_of (current_inferior);
+  ptid_t ptid = ptid_of (current_thread);
 
   gdb_assert (DR_FIRSTADDR <= regnum && regnum <= DR_LASTADDR);
 
@@ -615,7 +615,7 @@ static void
 x86_dr_low_set_control (unsigned long control)
 {
   /* Only update the threads of this process.  */
-  int pid = pid_of (current_inferior);
+  int pid = pid_of (current_thread);
 
   find_inferior (&all_threads, update_debug_registers_callback, &pid);
 }
@@ -625,7 +625,7 @@ x86_dr_low_set_control (unsigned long control)
 static unsigned long
 x86_dr_low_get_control (void)
 {
-  ptid_t ptid = ptid_of (current_inferior);
+  ptid_t ptid = ptid_of (current_thread);
 
   return x86_linux_dr_get (ptid, DR_CONTROL);
 }
@@ -636,7 +636,7 @@ x86_dr_low_get_control (void)
 static unsigned long
 x86_dr_low_get_status (void)
 {
-  ptid_t ptid = ptid_of (current_inferior);
+  ptid_t ptid = ptid_of (current_thread);
 
   return x86_linux_dr_get (ptid, DR_STATUS);
 }
@@ -1219,7 +1219,7 @@ x86_siginfo_fixup (siginfo_t *native, void *inf, int direction)
 {
 #ifdef __x86_64__
   unsigned int machine;
-  int tid = lwpid_of (current_inferior);
+  int tid = lwpid_of (current_thread);
   int is_elf64 = linux_pid_exe_is_elf_64_file (tid, &machine);
 
   /* Is the inferior 32-bit?  If so, then fixup the siginfo object.  */
@@ -1302,7 +1302,7 @@ x86_linux_read_description (void)
   static uint64_t xcr0;
   struct regset_info *regset;
 
-  tid = lwpid_of (current_inferior);
+  tid = lwpid_of (current_thread);
 
   is_elf64 = linux_pid_exe_is_elf_64_file (tid, &machine);
 
@@ -1475,7 +1475,7 @@ x86_arch_setup_process_callback (struct inferior_list_entry *entry)
   int pid = ptid_get_pid (entry->id);
 
   /* Look up any thread of this processes.  */
-  current_inferior
+  current_thread
     = (struct thread_info *) find_inferior (&all_threads,
 					    same_process_callback, &pid);
 
@@ -1488,7 +1488,7 @@ x86_arch_setup_process_callback (struct inferior_list_entry *entry)
 static void
 x86_linux_update_xmltarget (void)
 {
-  struct thread_info *save_inferior = current_inferior;
+  struct thread_info *saved_thread = current_thread;
 
   /* Before changing the register cache's internal layout, flush the
      contents of the current valid caches back to the threads, and
@@ -1497,7 +1497,7 @@ x86_linux_update_xmltarget (void)
 
   for_each_inferior (&all_processes, x86_arch_setup_process_callback);
 
-  current_inferior = save_inferior;
+  current_thread = saved_thread;
 }
 
 /* Process qSupported query, "xmlRegisters=".  Update the buffer size for