Added a TLI hook to signal that the target does not have or does not care about

Added a TLI hook to signal that the target does not have or does not care about
floating point exceptions, added use of flag to fold potentially exception
raising floating point math in selection DAG. No functionality change, as
targets have to explicitly ask for this behavior and none does today.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215222 91177308-0d34-0410-b5e6-96231b3b80d8