[RX] Add support for atomic operations

[Oleg Endo]

Hi,

The attached patch adds some rudimentary support for atomic operations.
 On the original RX there is one truly atomic insn "xchg".  All other
operations have to implement atomicity in some other way.  One straight
forward option which is already being done on SH is to disable
interrupts for the duration of the atomic sequence.  This works for
single-core systems that run in privileged mode.  And that's what the
patch does.

OK for trunk?

Cheers,
Oleg

gcc/ChangeLog:
	* config/rx/rx-protos.h (is_interrupt_func, is_fast_interrupt_func):
	Forward declare.
	(rx_atomic_sequence): New class.
	* config/rx/rx.c (rx_print_operand): Use symbolic names for PSW bits.
	(is_interrupt_func, is_fast_interrupt_func): Make non-static and
	non-inline.
	(rx_atomic_sequence::rx_atomic_sequence,
	rx_atomic_sequence::~rx_atomic_sequence): New functions.
	* config/rx/rx.md (CTRLREG_PSW, CTRLREG_USP, CTRLREG_FPSW, CTRLREG_CPEN,
	CTRLREG_BPSW, CTRLREG_BPC, CTRLREG_ISP, CTRLREG_FINTV,
	CTRLREG_INTB): New constants.
	(FETCHOP): New code iterator.
	(fethcop_name, fetchop_name2): New iterator code attributes.
	(QIHI): New mode iterator.
	(atomic_exchange<mode>, atomic_exchangesi, xchg_mem<mode>,
	atomic_fetch_<fetchop_name>si, atomic_fetch_nandsi,
	atomic_<fetchop_name>_fetchsi, atomic_nand_fetchsi): New patterns.
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