[analyzer] Refer to capture field to determine if capture is reference.

[analyzer] Refer to capture field to determine if capture is reference.

The analyzer incorrectly treats captures as references if either the original
captured variable is a reference or the variable is captured by reference.
This causes the analyzer to crash when capturing a reference type by copy
(PR24914). Fix this by refering solely to the capture field to determine when a
DeclRefExpr for a lambda capture should be treated as a reference type.

https://llvm.org/bugs/show_bug.cgi?id=24914
rdar://problem/23524412

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@253157 91177308-0d34-0410-b5e6-96231b3b80d8