Reinstate "FileCheck [5/12]: Introduce regular numeric variables"
This reinstates r360578 (git e47362c1ec1ea31b626336cc05822035601c3e57),
reverted in r360653 (git 004393681c25e34e921adccc69ae6378090dee54),
with a fix for the list added in FileCheck.rst to build without error.
- Linaro (changes up to diff 183612 of revision D55940)
- GraphCore (changes in later versions of revision D55940 and in new revision created off D55940)
Reviewers: jhenderson, chandlerc, jdenny, probinson, grimar,
Subscribers: hiraditya, llvm-commits, probinson, dblaikie, grimar,
arichardson, tra, rnk, kristina, hfinkel, rogfer01, JonChesterfield
Differential Revision: https://reviews.llvm.org/D60385