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

[dblaikie]

Summary

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)

cmake/modules/HandleLLVMOptions.cmake

if( MSVC )
 
   # Disable sized deallocation if the flag is supported. MSVC fails to compile
   # the operator new overload in User otherwise.
   check_c_compiler_flag("/WX /Zc:sizedDealloc-" SUPPORTS_SIZED_DEALLOC)
   append_if(SUPPORTS_SIZED_DEALLOC "/Zc:sizedDealloc-" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 
 elseif( LLVM_COMPILER_IS_GCC_COMPATIBLE )
   if (LLVM_ENABLE_WARNINGS)
-    append("-Wall -W -Wno-unused-parameter -Wwrite-strings" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+    append("-Wall -W -Wno-unused-parameter -Wwrite-strings -Wdeprecated" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
     append("-Wcast-qual" CMAKE_CXX_FLAGS)
 
     # Turn off missing field initializer warnings for gcc to avoid noise from
     # false positives with empty {}. Turn them on otherwise (they're off by
     # default for clang).
     check_cxx_compiler_flag("-Wmissing-field-initializers" CXX_SUPPORTS_MISSING_FIELD_INITIALIZERS_FLAG)
     if (CXX_SUPPORTS_MISSING_FIELD_INITIALIZERS_FLAG)
       if (CMAKE_COMPILER_IS_GNUCXX)