The Fuchsia zxtest library has ASSERT_DEATH but not EXPECT_DEATH.
The latter may be added in the future, but for now just use the
former as substitute.
Reviewed By: abrachet
Differential Revision: https://reviews.llvm.org/D156940
This part of the effort to make all test related pieces into the `test`
directory. This helps is excluding test related pieces in a straight
forward manner if LLVM_INCLUDE_TESTS is OFF. Future patches will also move
the MPFR wrapper and testutils into the 'test' directory.