[PATCH] Add support for generating MIPS legacy NaN

[Vladimir Radosavljevic]

================
Comment at: lib/Basic/Targets.cpp:5679
@@ +5678,3 @@
+  bool isNan2008() const override {
+    return IsNan2008 || isNaN2008Default();
+  }
----------------
dsanders wrote:
> This isn't quite right. It should just be IsNan2008 since IsNan2008 is initialized with the result of isNaN2008Default().
When you generating code for mips32r6/mips64r6 with option -mnan=legacy, IsNan2008 will be set to false.
In function handleTargetFeatures there are lines that change that.
      else if (*it == "-nan2008")
        IsNan2008 = false;
Because of that, I use the result of isNaN2008Default().

http://reviews.llvm.org/D7882

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