[binutils-gdb] Make dwarf_expr_context::stack_empty_p return a bool

[sergiodj+buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT eccd80d69487586578b7e085d8bd48657a4d7322 ***

Author: Simon Marchi <simon.marchi@ericsson.com>
Branch: master
Commit: eccd80d69487586578b7e085d8bd48657a4d7322

Make dwarf_expr_context::stack_empty_p return a bool

gdb/ChangeLog:

	* dwarf2expr.h (dwarf_expr_context) <stack_empty_p>: Change
	return type to bool.
	* dwarf2expr.c (dwarf_expr_context::stack_empty_p): Likewise.