PR29963, PDP11 link produces spurious relocation truncated messages

PDP11 is a 16-bit processor with 16-bit logical addresses.  Therefore
wrapping should be allowed on the 16-bit relocs, and may as well be
allowed for the 32-bit reloc too.

	PR 29963
	* pdp11.c (howto_table_pdp11): Use complain_overflow_dont.