Enable -Wdeprecated in the cmake build now that LLVM (& Clang, Polly, and LLD) are...

Enable -Wdeprecated in the cmake build now that LLVM (& Clang, Polly, and LLD) are -Wdeprecated clean

This particularly helps enforce the C++ Rule of 5 (for new move ops this
is already an error, but for a type only using C++98 features (copy
ctor/assign, dtor) it is only deprecated, not invalid)

Applying the flag for any GCC compatible compiler - GCC doesn't warn on
the Rule of 5 cases that C++11 deprecates, but it doesn't have other
false positives so far as I could see (compiling with GCC 4.8 didn't
produce any -Wdeprecated warnings I could spot).

Reviewers: aaron.ballman

Differential Revision: http://reviews.llvm.org/D13314

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@248963 91177308-0d34-0410-b5e6-96231b3b80d8