WholeProgramDevirt: fix access to a non-initialized field.

[krasin]

Summary

This is a follow up to r278389, where I have introduced the bug

[krasin]

Mehdi, submitting w/o a review, as I want to fix the ubsan bot:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fast/builds/15456/steps/check-llvm%20ubsan/

Please, feel free to add suggestions, I will create a follow up CL, if there're some.

[mehdi_amini]

This is trivial enough that you don't need pre-commit review.

llvm/trunk/include/llvm/Transforms/IPO/WholeProgramDevirt.h

 };
 
 // A virtual call target, i.e. an entry in a particular vtable.
 struct VirtualCallTarget {
   VirtualCallTarget(Function *Fn, const TypeMemberInfo *TM);
 
   // For testing only.
   VirtualCallTarget(const TypeMemberInfo *TM, bool IsBigEndian)
-      : Fn(nullptr), TM(TM), IsBigEndian(IsBigEndian) {}
+      : Fn(nullptr), TM(TM), IsBigEndian(IsBigEndian), WasDevirt(false) {}
 
   // The function stored in the vtable.
   Function *Fn;
 
   // A pointer to the type identifier member through which the pointer to Fn is
   // accessed.
   const TypeMemberInfo *TM;