The change to add explicitly-deleted constructors and assignemnt
operators in aead_test.cc and digest_test.cc broke GCC 4.8 builds.
Those changes were made to prevent MSVC from issuing these warnings:
* C4623: default constructor was implicitly defined as deleted
because a base class default constructor is inaccessible or
deleted.
* C4626: assignment operator was implicitly defined as deleted
because a base class assignment operator is inaccessible or
deleted.
* C5027: move assignment operator was implicitly defined as deleted
because a base class move assignment operator is inaccessible
or deleted.
All of these warnigns are just "Warning: we didn't do something
impossible in violation of the C++ language semantics" so they are safe
to disable. Even without considering the GCC 4.8 breakage, this is a
better fix.
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