...or rather, make the use of the default ABI explicit.  That seems
OK if not ideal for this heuristic.

In practical terms, the code patched here is counting GENERAL_REGS,
which are treated in the same way by all concurrent ABI variants
on AArch64.  It might give bad results if used for interrupt
handlers though.

2019-09-30  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* cfgloopanal.c: Include regs.h and function-abi.h.
	(init_set_costs): Use default_function_abi to test whether
	a general register is call-clobbered.

From-SVN: r276315