Fix warnings in FunctionTest.cpp.

Because of the goop involved in the EXPECT_EQ macro, we were getting the
following warning

  expression with side effects has no effect in an unevaluated context

because the "I++" was being used inside of a template type:

  switch (0) case 0: default: if (const ::testing::AssertionResult gtest_ar = (::testing::internal:: EqHelper<(sizeof(::testing::internal::IsNullLiteralHelper(Args[I++])) == 1)>::Compare("Args[I++]", "&A", Args[I++], &A))) ; else ::testing::internal::AssertHelper(::testing::TestPartResult::kNonFatalFailure, "../src/unittests/IR/FunctionTest.cpp", 94, gtest_ar.failure_message()) = ::testing::Message();

llvm-svn: 275291