Encapsulate FPOptions and use it consistently

Sema holds the current FPOptions which is adjusted by 'pragma STDC
FP_CONTRACT'.  This then gets propagated into expression nodes as they are
built.

This encapsulates FPOptions so that this propagation happens opaquely rather
than directly with the fp_contractable on/off bit.  This allows controlled
transitioning of fp_contractable to a ternary value (off, on, fast).  It will
also allow adding more fast-math flags later.

This is toward moving fp-contraction=fast from an LLVM TargetOption to a
FastMathFlag in order to fix PR25721.

Differential Revision: https://reviews.llvm.org/D31166

llvm-svn: 298877
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 668d4b2..4a9120b 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -11111,7 +11111,7 @@
     = new (S.Context) BinaryOperator(IterationVarRefRVal.build(S, Loc),
                      IntegerLiteral::Create(S.Context, Upper, SizeType, Loc),
                                      BO_NE, S.Context.BoolTy,
-                                     VK_RValue, OK_Ordinary, Loc, false);
+                                     VK_RValue, OK_Ordinary, Loc, FPOptions());
 
   // Create the pre-increment of the iteration variable.
   Expr *Increment