re PR c++/87093 (is_constructible (__is_constructible() instrinsic) explicitly instantiates conversion member function of source)

PR c++/87093

gcc/cp

PR c++/87093
* method.c (constructible_expr): We're in an unevaluated context
in all cases, not just for class targets.

testsuite/

PR c++/87093
* g++.dg/ext/is_constructible2.C: New.

From-SVN: r264253