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/Frontend/Rewrite/RewriteModernObjC.cpp b/clang/lib/Frontend/Rewrite/RewriteModernObjC.cpp
index e6469f5..8871bb7 100644
--- a/clang/lib/Frontend/Rewrite/RewriteModernObjC.cpp
+++ b/clang/lib/Frontend/Rewrite/RewriteModernObjC.cpp
@@ -7500,7 +7500,7 @@
       BinaryOperator *addExpr = 
         new (Context) BinaryOperator(castExpr, DRE, BO_Add, 
                                      Context->getPointerType(Context->CharTy),
-                                     VK_RValue, OK_Ordinary, SourceLocation(), false);
+                                     VK_RValue, OK_Ordinary, SourceLocation(), FPOptions());
       // Don't forget the parens to enforce the proper binding.
       ParenExpr *PE = new (Context) ParenExpr(SourceLocation(),
                                               SourceLocation(),