[PATCH, libgfortran] PR 67585 Handle EINTR

[FX]

> Many POSIX systems have the bad habit of not restarting interrupted
> syscalls. On these systems it's up to the user to check for an error
> with errno == EINTR and restart manually. This patch does this for
> libgfortran, so that GFortran users don't have to do it.

I have not much experience with EINTR, but is it garanteed that those EINTR loops will never cycle forever?

Apart from that, OK to commit.

FX