Add ARM/thumb attribute target

Add ARM/thumb attribute target

	PR target/52144

	* config/arm/arm.opt (THUMB, arm_restrict_it, inline_asm_unified): Save.
	* config/arm/arm-protos.h (arm_valid_target_attribute_tree): Declare.
	(arm_reset_previous_fndecl, arm_change_mode_p): Likewise.
	* config/arm/arm.h (SWITCHABLE_TARGET): Define.
	* config/arm/arm.c (arm_reset_previous_fndecl): New functions.
	(arm_valid_target_attribute_tree, arm_change_mode_p): Likewise.
	(arm_valid_target_attribute_p): Likewise.
	(arm_set_current_function, arm_can_inline_p): Likewise.
	(arm_valid_target_attribute_rec): Likewise.
	(arm_previous_fndecl): New variable.
	(TARGET_SET_CURRENT_FUNCTION, TARGET_OPTION_VALID_ATTRIBUTE_P): Define.
	(TARGET_CAN_INLINE_P): Define.
	(arm_asm_trampoline_template): Emit mode.
	(arm_file_start): Don't set unified syntax.
	(arm_declare_function_name): Set unified syntax and mode.
	(arm_option_override): Init target_option_default_node.
	and target_option_current_node.
	* config/arm/arm.md (*call_value_symbol): Set mode when possible.
	(*call_symbol): Likewise.
	* doc/extend.texi: Document ARM/Thumb target attribute.
	* doc/invoke.texi: Likewise.

	* gcc.target/arm/attr_arm.c: New test
	* gcc.target/arm/attr_arm-err.c: New test
	* gcc.target/arm/attr_thumb.c: New test
	* gcc.target/arm/attr_thumb-static.c: New test

From-SVN: r224314