The assert added to EmitCall there was triggering in Windows Chromium
builds, due to a mismatch of the return type.
The MSVC constructor call extension (this->Foo::Foo()) was emitting
the constructor call from 'EmitCXXMemberOrOperatorMemberCallExpr' via
calling 'EmitCXXMemberOrOperatorCall', instead of
'EmitCXXConstructorCall'. On targets where HasThisReturn is true, that
was failing to set the proper return type in the call info.
Switching to calling EmitCXXConstructorCall also allowed removing some
code e.g. the trivial copy/move support, which is already handled in