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
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 68f27ee..91917cf 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1336,6 +1336,7 @@
     Opts.ZVector = 0;
     Opts.CXXOperatorNames = 1;
     Opts.LaxVectorConversions = 0;
+    Opts.DefaultFPContract = 1;
     Opts.NativeHalfType = 1;
   }