[PR c++/85027] deal with baselink in save_expr in instantiate_type

[PR c++/85027] deal with baselink in save_expr in instantiate_type

We use SAVE_EXPRs in conditional expressions without the middle
operand, to evaluate the first operand only once.  When the conversion
of the first operand fails, we may call instantiate_type get a better
error message.  We have code to peel off the SAVE_EXPR there, but then
we may end up with a BASELINK, and we're past the code that deals with
BASELINKs.  Reorder the tests so that we expose the saved expr first,
and then deal with BASELINKs.

for  gcc/cp/ChangeLog

	PR c++/85027
	* class.c (instantiate_type): Peel off SAVE_EXPR before
	BASELINK.

for  gcc/testsuite/ChangeLog

	PR c++/85027
	* g++.dg/pr85027.C: New.

From-SVN: r258989