In this PR, the constexpr evaluator was confused by a parameter that 
changed to a reference type after the constant expression body was saved 
for later evaluation; we ended up trying to evaluate an address of an 
address, since we added one address on the caller side to pass to the 
invisible reference and another on the callee side to pass the value 
parameter to a reference parameter.  Fixed by stripping the reference on 
the caller side.

Tested x86_64-pc-linux-gnu, applying to trunk.