Add low-level option for avoiding float stores from va_start until
soft-float is properly supported.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215221 91177308-0d34-0410-b5e6-96231b3b80d8
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