[flang-commits] [flang] [flang][docs] Update llvm-test-suite docs (PR #81596)

[David Spickett via flang-commits]

DavidSpickett wrote:

The header file is in the build tree, but flang doesn't find it:
```
$ find -name ISO_Fortran_binding.h
./lib/clang/19/include/ISO_Fortran_binding.h
```
Is that expected?

https://github.com/llvm/llvm-project/pull/81596