Move encoded as 'or' in binutils.

Move encoded as 'or' in binutils.

A patch (http://sourceware.org/ml/binutils/2015-07/msg00376.html)
submitted to binutils will be encoding move as an 'or' instruction over
[d]addu in assembly and various code stubs. This patch for gdb addresses
that change for the mips specific parts of gdb.

gdb/ChangeLog:

	* mips-linux-tdep.c (mips_linux_in_dynsym_stub): Recognise 'or'
	as move along with [d]addu.