Add custom HTM fast path for RTM on x86_64.

Add custom HTM fast path for RTM on x86_64.

	* libitm_i.h (gtm_thread): Assign an asm name to serial_lock.
	(htm_fastpath): Assign an asm name.
	* libitm.h (_ITM_codeProperties): Add non-ABI flags used by custom
	HTM fast paths.
	(_ITM_actions): Likewise.
	* config/x86/target.h (HTM_CUSTOM_FASTPATH): Enable custom fastpath on
	x86_64.
	* config/x86/sjlj.S (_ITM_beginTransaction): Add custom HTM fast path.
	* config/posix/rwlock.h (gtm_rwlock): Update comments.  Move summary
	field to the start of the structure.
	* config/linux/rwlock.h (gtm_rwlock): Update comments.
	* beginend.cc (gtm_thread::begin_transaction): Add retry policy
	handling for custom HTM fast paths.

From-SVN: r202101