[clang] [C2y] Handle FP-suffixes on prefixed octals (#141230) (PR #141695)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

I added @cor3ntin and @tahonermann for some extra sets of eyes, seeing as how I already messed this up once before. :-)

https://github.com/llvm/llvm-project/pull/141695