The i128 suffix isn't always available.

This Lexer test unconditionally used the i128 integer literal suffix.
This suffix is only available to targets that have 128-bit arithmetic
support.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@211446 91177308-0d34-0410-b5e6-96231b3b80d8