Write CodeView information about optimized stack variables

Write CodeView information about optimized stack variables

Outputs S_DEFRANGE_REGISTER_REL symbols for optimized local variables that are
on the stack, consisting of the stack register, the offset, and the code range
for which this applies.

gcc/
	* dwarf2codeview.cc (enum cv_sym_type): Add S_DEFRANGE_REGISTER_REL.
	(write_defrange_register_rel): New function.
	(write_optimized_local_variable_loc): Add fbloc param, and call
	write_defrange_register_rel.
	(write_optimized_local_variable): Add fbloc param.
	(write_optimized_function_vars): Add fbloc param.