Add support for tracing through shared libraries.

	* configure.ac: Check for link.h and dl_iterate_phdr.
	* elf.c: #include <link.h> if system has dl_iterate_phdr.  #undef
	ELF macros before #defining them.
	(dl_phdr_info, dl_iterate_phdr): Define if system does not have
	dl_iterate_phdr.
	(struct elf_syminfo_data): Add next field.
	(elf_initialize_syminfo): Initialize next field.
	(elf_add_syminfo_data): New static function.
	(elf_add): New static function, broken out of
	backtrace_initialize.  Call backtrace_dwarf_add instead of
	backtrace_dwarf_initialize.
	(struct phdr_data): Define.
	(phdr_callback): New static function.
	(backtrace_initialize): Call elf_add.
	* dwarf.c (struct dwarf_data): Add next and base_address fields.
	(add_unit_addr): Add base_address parameter.  Change all callers.
	(add_unit_ranges, build_address_map): Likewise.
	(add_line): Add ddata parameter.  Change all callers.
	(read_line_program, add_function_range): Likewise.
	(dwarf_lookup_pc): New static function, broken out of
	dwarf_fileline.
	(dwarf_fileline): Call dwarf_lookup_pc.
	(build_dwarf_data): New static function.
	(backtrace_dwarf_add): New function.
	(backtrace_dwarf_initialize): Remove.
	* internal.h (backtrace_dwarf_initialize): Don't declare.
	(backtrace_dwarf_add): Declare.
	* configure, config.h.in: Rebuild.

From-SVN: r192267