Introduce field_unsigned

Introduce field_unsigned

This adds field_unsigned and changes various places using field_fmt
with "%u" to use this instead.  This also replaces an existing
equivalent helper function in record-btrace.c.

2019-07-15  Tom Tromey  <tromey@adacore.com>

	* mi/mi-out.h (class mi_ui_out) <do_field_unsigned>: Declare.
	* mi/mi-out.c (mi_ui_out::do_field_unsigned): New method.
	* cli-out.h (class cli_ui_out) <do_field_unsigned>: Declare.
	* cli-out.c (cli_ui_out::do_field_int): New method.
	* ui-out.c (ui_out::field_unsigned): New method.
	* symfile.c (generic_load): Use field_unsigned.
	(print_transfer_performance): Likewise.
	* record-btrace.c (ui_out_field_uint): Remove.
	(btrace_call_history_insn_range, btrace_call_history): Use
	field_unsigned.
	* disasm.c (gdb_pretty_print_disassembler::pretty_print_insn): Use
	field_unsigned.
	* ui-out.h (class ui_out) <field_unsigned>: New method.
	<do_field_unsigned>: Likewise.