dwarf2read: Restrict ICC workaround to ICC<14

dwarf2read: Restrict ICC workaround to ICC<14

GDB has a workaround for DWARF output by ICC, related to missing
DW_AT_declaration on incomplete types.  The bug was fixed in ICC 14,
so this commit adjusts GDB accordingly.

For the version check, this adds a new parser function for the ICC
producer string.  While at it, it also adds unit tests for the
producer parsing covering the new function and preexisting parsers.

gdb/ChangeLog:
2017-09-26  Walfred Tedeschi  <walfred.tedeschi@intel.com>
	    Pedro Alves <palves@redhat.com>

	* dwarf2read.c (dwarf2_cu): Remove field producer_is_icc and add
	producer_is_icc_lt_14.
	(producer_is_icc_lt_14): New function.
	(check_producer): Add code for checking version of ICC.
	(producer_is_icc): Move to producer.c.
	(read_structure_type): Restrict ICC workaround to ICC<14.
	* producer.c: Include selftest.h.
	(producer_is_icc, producer_parsing_tests, _initialize_producer):
	New functions.
	* producer.h (producer_is_icc): New declaration.