Enhance abseil-faster-strsplit-delimiter to handle other non-printable characters.

Summary:
Currently it fails on cases like '\001'.

Note: Since `StringLiteral::outputString` dumps most nonprintable
characters in octal value, the exact string literal format isn't preserved,
e.g. `"\x01"` becomes `'\001'`.

Reviewers: gribozavr

Reviewed By: gribozavr

Subscribers: lebedev.ri, Eugene.Zelenko, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D64151

Patch by Xiaoyi Zhang.

llvm-svn: 365463