Some systems set an artificially low soft limit on open file count,
for compatibility with code that uses select and its hard-coded
maximum file descriptor (limited by the size of fd_set).
Go does not use select, so it should not be subject to these limits.
On some systems the limit is 256, which is very easy to run into, even
in simple programs like gofmt when they parallelize walking a file tree.
After a long discussion on go.dev/issue/46279, we decided the best
approach was for Go to raise the limit unconditionally for itself, and
then leave old software to set the limit back as needed. Code that
really wants Go to leave the limit alone can set the hard limit, which
Go of course has no choice but to respect.