darwin, testsuite - fix PR 63891.

This is a testcase failing because one part of the codegen is
(correctly) generating the scan-asm-not signature.

Fixed by altering the build options.

gcc/testsuite/

2019-05-18  Iain Sandoe  <iain@sandoe.co.uk>

	PR target/63891
	* gcc.dg/darwin-weakimport-3.c: Adjust options and explain
	the reasons.

From-SVN: r271474

gcc/testsuite/ChangeLog

+2019-05-18  Iain Sandoe  <iain@sandoe.co.uk>
+
+	PR target/63891
+	* gcc.dg/darwin-weakimport-3.c: Adjust options and explain
+	the reasons.
+
 2019-05-21  Uroš Bizjak  <ubizjak@gmail.com>
 
 	* gcc.target/i386/vect-signbitf.c: New test.

gcc/testsuite/gcc.dg/darwin-weakimport-3.c

 /* { dg-do compile { target *-*-darwin* } } */
-/* { dg-options "-fno-asynchronous-unwind-tables" } */
+
+/* Here we want to test if "foo" gets placed into a coalesced
+   section (it should not).
+
+   However, for i386, and PIC code we have a "get_pc thunk" that
+   is (correctly) placed in a coalesced section when using an older
+   linker - also unwind tables are emitted into coalesced.
+
+   With modern linkers this is moot, since even weak symbols
+   are emitted into the regular sections.
+
+   To avoid the unwind tables -fno-asynchronous-unwind-tables.
+   To ensure that we emit code for an older linker -mtarget-linker
+   To avoid the get_pc thunk optimise at least O1.  */
+
+/* { dg-options "-fno-asynchronous-unwind-tables -O1 -mtarget-linker 85.2" } */
 /* { dg-require-weak "" } */
 
 /* { dg-final { scan-assembler-not "coalesced" } } */