[NFC] Silence warning about ptr-to-func to ptr-to-obj cast in clang-fuzzer/handle...

[NFC] Silence warning about ptr-to-func to ptr-to-obj cast in clang-fuzzer/handle-llvm/handle_llvm.cpp.

Summary:
I don't have the whole list of GCC binaries available so I determined the exact
version where the warning disappeared via:

https://github.com/gcc-mirror/gcc/blob/gcc-4_9_0-release/gcc/cp/typeck.c#L6863
https://github.com/gcc-mirror/gcc/blob/gcc-4_8_5-release/gcc/cp/typeck.c#L6652

Reviewers: emmettneyman, erichkeane

Reviewed By: emmettneyman, erichkeane

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D50056

llvm-svn: 338551