gdb/dwarf: Convert some predicates from int to bool

gdb/dwarf: Convert some predicates from int to bool

In the dwarf reader we have a set of predicates, these include the
different producer predicates and also some control predicates. The
older ones are declared as integers, while newer ones (added since the
C++ conversion) are bool.

This commit makes them all bool for consistency.  There should be no
user visible change after this commit.

gdb/ChangeLog:

	* dwarf2read.c (struct dwarf2_cu): Convert the fields 'mark',
	'has_loclist', 'checked_producer', 'producer_is_gxx_lt_4_6',
	'producer_is_gcc_lt_4_3', 'producer_is_icc_lt_14',
	'processing_has_namespace_info' from unsigned int to bool.  Update
	comments.
	(producer_is_icc_lt_14): Update return type.
	(producer_is_gcc_lt_4_3): Likewise.
	(producer_is_gxx_lt_4_6): Likewise.
	(process_die): Write true instead of 1 into predicate fields.
	(dwarf2_start_symtab): Likewise.
	(var_decode_location): Likewise.
	(dwarf2_mark_helper): Likewise.
	(dwarf2_mark): Likewise.
	(dwarf2_clear_marks): Write false instead of 0 into predicate
	field.
	(dwarf2_cu::dwarf2_cu): Initialise predicate fields to false, not
	0.