Merge MIPS dl-lookup.c into generic file.

MIPS has its own version of dl-lookup.c to deal with differences
between undefined symbol semantics in the PIC and non-PIC ABIs.  This
is often liable to get out of date with respect to the generic file
(for example, the recent __builtin_expect changes didn't cover ports,
and it's not obvious to anyone changing dl-lookup.c that there would
be architecture-specific versions).

This patch adds a macro that dl-machine.h can define that is used in
the appropriate place in dl-lookup.c, so that MIPS no longer needs its
own version of that file.

Tested for mips64 that the only changes to disassembly of installed
shared libraries appear to be ld.so changes attributable to different
line numbers and paths in assertions.

	* elf/dl-lookup.c (ELF_MACHINE_SYM_NO_MATCH): Define if not
	already defined.
	(do_lookup_x): Use ELF_MACHINE_SYM_NO_MATCH.
	* sysdeps/mips/dl-lookup.c: Remove.
	* sysdeps/mips/dl-machine.h (ELF_MACHINE_SYM_NO_MATCH): New macro.