config, btrace: check for pt_insn_event in libipt

config, btrace: check for pt_insn_event in libipt

Version 2 of libipt adds an event system to instruction flow decoders and
deprecates indicating events via flags in struct pt_insn.  Add configuration
checks to determine which version we have.

gdb/
	* configure.ac: Check for pt_insn_event, struct pt_insn.enabled,
	and struct pt_insn.resynced.
	* configure: Regenerated.
	* config.in: Regenerated.