Use EXPECT_FALSE instead of EXPECT_EQ(false, ...

Commit https://reviews.llvm.org/rL324489 added

    EXPECT_EQ(false, N->isUnsigned());

which older GCC versions dislike for some reason. Anyway, it looks like the
proper GTest way is to use EXPECT_FALSE, etc.


Differential Revision: https://reviews.llvm.org/D43233

llvm-svn: 325121