BFD/DWARF2: Correct an `index' global shadowing error

BFD/DWARF2: Correct an `index' global shadowing error

Fix a commit 089e3718bd8d ("Greatly improve the speed if looking up
DWARF line number information.") build regression:

cc1: warnings being treated as errors
.../bfd/dwarf2.c: In function 'build_line_info_table':
.../bfd/dwarf2.c:1614: warning: declaration of 'index' shadows a global declaration
/usr/include/string.h:304: warning: shadowed declaration is here
.../bfd/dwarf2.c: In function 'build_lookup_funcinfo_table':
.../bfd/dwarf2.c:2262: warning: declaration of 'index' shadows a global declaration
/usr/include/string.h:304: warning: shadowed declaration is here
make[4]: *** [dwarf2.lo] Error 1

in a way following commit 91d6fa6a035c ("Add -Wshadow to the gcc command
line options used when compiling the binutils.").

	bfd/
	* dwarf2.c (build_line_info_table): Rename `index' local
	variable to `line_index'.
	(build_lookup_funcinfo_table): Rename `index' local variable to
	`func_index'.