stop defining linkrelax in multiple places

stop defining linkrelax in multiple places

Defining linkrelax to have different values in as.c and tc-msp430.c /
tc-mn10300.c is at least rather tricky, and seems fragile, when we can just set
it in md_begin instead.

gas/ChangeLog:

2016-05-16  Trevor Saunders  <tbsaunde+binutils@tbsaunde.org>

	* config/tc-mn10300.c (md_begin): set linkrelax here instead of
	defining it.
	* config/tc-msp430.c (md_begin): Likewise.