Revert "Make FP_CONTRACT ON the default."

This reverts commit r253269.

This leads to assert / segfault triggering on the following reduced example:
float foo(float U, float base, float cell) { return (U = 2 * base) - cell; }

llvm-svn: 253337

clang/lib/Frontend/CompilerInvocation.cpp

@@ -1336,6 +1336,7 @@ void CompilerInvocation::setLangDefaults(LangOptions &Opts, InputKind IK,
     Opts.ZVector = 0;
     Opts.CXXOperatorNames = 1;
     Opts.LaxVectorConversions = 0;
+    Opts.DefaultFPContract = 1;
     Opts.NativeHalfType = 1;
   }