Suppress GCC 8 warnings from LLVM in ClingUtils

include/llvm/ADT/SmallVector.h:296:13: warning:
‘void* memcpy(void*, const void*, size_t)’ writing to an object of type
‘struct std::pair<clang::CXXMethodDecl*, const clang::FunctionProtoType*>’
with no trivial copy-assignment; use copy-assignment or copy-initialization
instead [-Wclass-memaccess]

       memcpy(Dest, I, (E - I) * sizeof(T));
       ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~