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/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index ed405b5..c0cbde2 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -6074,7 +6074,7 @@
                                                       T, E->getValueKind(),
                                                       E->getObjectKind(),
                                            Importer.Import(E->getOperatorLoc()),
-                                                      E->isFPContractable());
+                                                      E->getFPFeatures());
 }
 
 Expr *ASTNodeImporter::VisitConditionalOperator(ConditionalOperator *E) {
@@ -6224,7 +6224,7 @@
                                                E->getObjectKind(),
                                                CompLHSType, CompResultType,
                                            Importer.Import(E->getOperatorLoc()),
-                                               E->isFPContractable());
+                                               E->getFPFeatures());
 }
 
 bool ASTNodeImporter::ImportCastPath(CastExpr *CE, CXXCastPath &Path) {