Add a target hook for FLT_EVAL_METHOD and use it to set the value on x86 with sse disabled.

x87 math evaluates everything with 80 bits precision, so we have to set FLT_EVAL_METHOD
to "2".

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@147311 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed