c++: value category of compound object expr [PR104173]

c++: value category of compound object expr [PR104173]

Here the call to (the &&-qualified) toLower() is incorrectly rejected
during overload resolution because the object expression is encoded as
an lvalue when it's really a prvalue.  The object expression,
instance()->applicationName(), is encoded as an INDIRECT_REF of a
COMPOUND_EXPR

  *(*instance ();, &TARGET_EXPR <D.2383, QCoreApplication::applicationName ()>;);

which lvalue_kind deems an lvalue.

This issue is similar to PR88103 except that here the original compound
object expression is a prvalue rather than an xvalue.  The fix there was to
adjust the result of unary_complex_lvalue in build_class_member_access_expr
so that xvalueness of the original expression is preserved.  This patch
extends that fix so that rvalueness is preserved more generally.

	PR c++/104173

gcc/cp/ChangeLog:

	* typeck.cc (build_class_member_access_expr): Extend
	unary_complex_lvalue result adjustment to preserve all
	rvalues, not just xvalues.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/ref-qual21.C: New test.