[clang] [flang] [flang][driver] Rename `flang-new` as `flang` (PR #74377)

[Brad Smith via cfe-commits]

brad0 wrote:

> ok, but is there some threshold of percent that pass, or a specific list that we want to be sure pass? My understanding is that we've been running (at least a subset of) the gfortran test suite for a while now. What makes the current results not sufficient?

I think it's more of take flang-new and run it through the test suite and provide the output results.

https://github.com/llvm/llvm-project/pull/74377