Enhance the diagnostic for literal float -> int conversions to suggest
rewriting the literal when the value is integral. It is not uncommon to
see code written as:

  const int kBigNumber = 42e5;

Without any real awareness that this is no longer an ICE. The note helps
automate and ease the process of fixing code that violates the warning.

llvm-svn: 129243
GitOrigin-RevId: 016ef400c41fee3ba8036c0e8ef26cb48f9365f5