Fortran filesystem

Generally use C99 functions except for functions directly using C++17 <filesystem> functions. This improves internal quality and maintenance by deduplicating code between C and C++ interfaces. We also broke up the source code into more internal source files for readability and IWYU clarity.

added functions fs_is_optimized() fs_cpu_arch() fs_is_android()

added optional "ok" argument to Fortran call touch(file, ok) and had touch() check that file is created--on Windows CI for example, touch would succeed, but the file wasn't actually created.