[Flang] Fix parsing error on loop count compiler directive

[mnadeem]

Summary

Fixes:
https://github.com/llvm/llvm-project/issues/58731
https://github.com/llvm/llvm-project/issues/56678

Only handles this form which was reported: !DIR$ LOOP COUNT (n1[, n2]...)

[klausler]

flang/lib/Parser/Fortran-parsers.cpp

1219

Two minor comments: I used "ignore_tkr" for the IGNORE_TKR directive parser since it actually has an underscore in its name. LOOP COUNT does not, so "loopCount" would be a better name.

Second, be sure to run your modified code through clang-format 16.x before merging.

[sscalpone]

@mnadeem Please update the documentation llvm-project/flang/docs/Directives.md to include dir$ loop count. Thank you!

[mnadeem]

In D141976#4061262, @sscalpone wrote:

@mnadeem Please update the documentation llvm-project/flang/docs/Directives.md to include dir$ loop count. Thank you!

This directive is parsed but ignored, should I still add it to Directives.md?