unwind fix for musl

On behalf of szabolcs.nagy@arm.com

2015-04-22  Gregor Richards  <gregor.richards@uwaterloo.ca>
	    Szabolcs Nagy  <szabolcs.nagy@arm.com>

	* unwind-dw2-fde-dip.c (USE_PT_GNU_EH_FRAME): Define it on
	Linux if target provides dl_iterate_phdr.

Co-Authored-By: Szabolcs Nagy <szabolcs.nagy@arm.com>

From-SVN: r222328