[PATCH 0/2] Support libc with stdio-only I/O in libstdc++

[Keith Packard]

The current libstdc++ basic_file_stdio.cc code assumes a POSIX API
underneath the stdio implementation provided by the host libc. This
means that the host must provide a fairly broad POSIX file API,
including read, write, open, close, lseek and ioctl.

This patch changes basic_file_stdio.cc to only use basic ANSI-C stdio
functions, allowing it to be used with libc implementations like
picolibc which may not have a POSIX operating system underneath.

This is version 2 of the patch. This version uses the existing
--enable-stdio option, extending that to add 'stdio_pure' for this
mode using a patch created by Jonathan Wakely <jwakely@redhat.com>