gdb/

gdb/
	* arm-tdep.h (arm_insert_single_step_breakpoint): Add prototype.
	* arm-tdep.c (arm_override_mode): New global.
	(arm_pc_is_thumb): Respect arm_override_mode.  Remove single-step
	execution mode heuristics.
	(thumb_get_next_pc_raw): Remove INSERT_BKTP argument; always insert
	second single-step breakpoint if needed, using
	arm_insert_single_step_breakpoint.
	(arm_get_next_pc_raw): Remove INSERT_BKTP argument.  Only handle
	ARM execution mode, do not call thumb_get_next_pc_raw.
	(arm_get_next_pc): Encode execution mode in return value.  Call
	either arm_get_next_pc_raw or thumb_get_next_pc_raw.
	(arm_insert_single_step_breakpoint): New function.
	(arm_software_single_step): Call it.
	* arm-linux-tdep.c (arm_linux_sigreturn_return_addr): Add IS_THUMB
	argument to return execution mode of sigreturn target.
	(arm_linux_syscall_next_pc): Use it.
	(arm_linux_copy_svc): Update call.
	(arm_linux_software_single_step): Call
	arm_insert_single_step_breakpoint.

gdb/testsuite/
	* gdb.arch/thumb-singlestep.S: New file.
	* gdb.arch/thumb-singlestep.exp: Likewise.