When bfd/pdp11.c was copied from bfd/aoutx.h, the #defines for external symbol types...

When bfd/pdp11.c was copied from bfd/aoutx.h, the #defines for external symbol types N_TEXT etc. were #undef'd and then #define'd with new values.  But N_STAB was not changed even though the new value for N_EXT overlapped with it.  This caused aout_link_write_symbols() to treat global symbols referenced in the source but defined in a linker script as undefined.

Separately, in translate_symbol_table() the 16-bit symbol values were sign extended to unsigned long (e.g., 64 bits) when they really should be treated as unsigned so the value remains 16 bits.

	PR 25828
	* pdp11.c (N_STAB): Modify value to avoid conflict with N_EXT
	causing globals from linker script to be treated as debug symbols.
	(translate_symbol_table): Don't sign-extend symbol values from 16
	to 64 bits in nm output.