c++: assignment to temporary [PR59950]

c++: assignment to temporary [PR59950]

Given build_this of a TARGET_EXPR, cp_build_fold_indirect_ref returns the
TARGET_EXPR.  But that's the wrong value category for the result of the
defaulted class assignment operator, which returns an lvalue, so we need to
actually build the INDIRECT_REF.

	PR c++/59950

gcc/cp/ChangeLog:

	* call.cc (build_over_call): Use cp_build_indirect_ref.

gcc/testsuite/ChangeLog:

	* g++.dg/init/assign2.C: New test.