The istantiate2.C test has started to fail since Darwin's impl. of
this part of the ABI was fixed. It now emits the same output as
other platforms (and clang).

2019-05-02  Iain Sandoe  <iain@sandoe.co.uk>

	* g++.dg/ext/instantiate2.C: Remove special-caseing for Darwin.

From-SVN: r270801