dwarf.c: string_fortify.h strncpy error

dwarf.c: string_fortify.h strncpy error

In function 'strncpy',
    inlined from 'display_debug_lines_decoded' at /home/alan/src/binutils-gdb/binutils/dwarf.c:5434:5,
    inlined from 'display_debug_lines' at /home/alan/src/binutils-gdb/binutils/dwarf.c:5567:21:
/usr/include/bits/string_fortified.h:95:10: error: '__builtin_strncpy' specified bound 36 equals destination size [-Werror=stringop-truncation]

No need for strncpy here, the string being copied always fits the
destination buffer.

	* dwarf.c (display_debug_lines_decoded): Use memcpy rather than
	strncpy when trimming file name length to MAX_FILENAME_LENGTH.
	Don't make an unnecessary copy when length is good.