libbacktrace: support returning discriminator field

Based on patch from Andi Kleen.

	* backtrace.h (backtrace_create_state): Rewrite comment to change
	threaded parameter to flags.
	(backtrace_full_callback, backtrace_syminfo_callback): Document
	behavior change if moredata flag is set.
	(struct backtrace_moredata): Define.
	* backtrace-supported.h.in (BACKTRACE_SUPPORTS_MOREDATA): Define.
	* internal.h (struct backtrace_state): Add moredata field.
	(BACKTRACE_MOREDATA_VERSION): Define.
	* state.c (backtrace_create_state): Change threaded parameter to
	flags.  Set state moredata field based on flags.
	* dwarf.c (struct line): Add disc field.
	(struct function): Add caller_disc field.
	(call_callback): New static function.
	(add_line): Add disc parameter.  Change all callers.  Store disc
	in new line value.
	(read_line_program): Track discriminator value.
	(read_line_info): Initialize disc field in final line entry.
	(read_function_entry): Handle DW_AT_GNU_discriminator.
	(report_inlined_functions): Add disc parameter. Change all
	callers. Call call_callback rather than calling callback
	directly.
	(dwarf_lookup_pc): Handle inlined discriminators. Call
	call_callback rather than calling callback directly.
	(dwarf_fileline): Call call_callback rather than calling callback
	directly.
	* elf.c (elf_syminfo): Pass moredata if requested.
	* macho.c (macho_syminfo): Likewise.
	* pecoff.c (coff_syminfo): Likewise.
	* xcoff.c (xcoff_syminfo): Likewise.
	(xcoff_lookup_pc): Likewise.
	* backtrace.c: #include <string.h>.
	(unwind): Pass moredata if requested.
	* unknown.c: #include <string.h>.
	(unknown_fileline): Pass moredata if requested.
	* fileline.c (backtrace_syminfo_to_full_callback): Add comment
	about moredata.
	* mdtest.c: New test file.
	* Makefile.am (mdtest_SOURCES): Define.
	(mdtest_CFLAGS, mdtest_LDFLAGS, mdtest_LDADD): Define.
	(BUILDTESTS): Add mdtest.
	* Makefile.in: Regenerate.