Add tests for the new record-btrace target.

testsuite/
	* Makefile.in: Add btrace testsuite.
	* configure: Regenerated.
	* configure.ac: Add btrace testsuite.
	* gdb.btrace/Makefile.in: New file.
	* gdb.btrace/enable.c: New file.
	* gdb.btrace/enable.exp: New file.
	* gdb.btrace/function_call_history.c: New file.
	* gdb.btrace/function_call_history.exp: New file.
	* gdb.btrace/instruction_history.c: New file.
	* gdb.btrace/instruction_history.exp: New file.
	* gdb.btrace/instruction_history.S: New file.
	* lib/gdb.exp: Add btrace skip proc.