Fix coff-pe-read.c to compile with Wunused.

	Fix coff-pe-read.c to compile with Wunused.

	* coff-pe-read.c (add_pe_exported_sym): Remove unused 'dll_name_len'.
	(add_pe_forwarded_sym): Remove unused 'section', 'dll_name_len'.
	(read_pe_exported_syms): Remove unused 'exportix'.
	(pe_text_section_offset): Remove unused 'opthdr_ofs', 'num_entries',
	'export_rva', 'export_size', 'expptr', 'exp_funcbase', 'expdata',
	'erva', 'name_rvas', 'ordinals', 'nexp', 'ordbase', 'dll_name'.

	Reference: http://sourceware.org/ml/gdb-patches/2013-03/msg01081.html