libdw: Don't use INTUSE in libdwP.h str_offsets_base_off

libdw: Don't use INTUSE in libdwP.h str_offsets_base_off

readelf.c cheats and include libdwP.h, which is an internal only
header of libdw. It really shouldn't do that, but there are some
internals that readelf currently needs. The str_offsets_base_off
function used by readelf uses INTUSE when calling dwarf_get_units.
This is a micro optimization useful inside libdw so a public
function can be called directly, skipping a PLT call. This can
cause issues linking readelf since it might not be able to call
the internal function, since readelf.c isn't part of libdw itself.
Just drop the INTUSE.

	* libdw/libdwP.h (str_offsets_base_off): Don't use INTUSE
	when calling dwarf_get_units.

Signed-off-by: Mark Wielaard <mark@klomp.org>