musl: Fix invalid tls model in libgomp and libitm PR91938

Musl does not support initial-exec tls in dynamically loaded shared
libraries.

libgomp/ChangeLog:

2019-12-03  Szabolcs Nagy  <szabolcs.nagy@arm.com>

	PR libgomp/91938
	* configure.tgt: Avoid IE tls on *-*-musl*.

libitm/ChangeLog:

2019-12-03  Szabolcs Nagy  <szabolcs.nagy@arm.com>

	PR libgomp/91938
	* configure.tgt: Avoid IE tls on *-*-musl*.

From-SVN: r278932