Make gdb_flush also flush the wrap buffer

Make gdb_flush also flush the wrap buffer

This changes gdb_flush to also flush the internal wrap buffer.  A few
places needed to continue using the previous approach, so this also
introduces ui_file_flush for those.

gdb/ChangeLog
2020-02-05  Iain Buclaw  <ibuclaw@gdcproject.org>

        * gdb/event-loop.c (gdb_wait_for_event): Update.
        * gdb/printcmd.c (printf_command): Update.
        * gdb/remote-fileio.c (remote_fileio_func_write): Update.
        * gdb/remote-sim.c (gdb_os_flush_stdout): Update.
        (gdb_os_flush_stderr): Update.
        * gdb/remote.c (remote_console_output): Update.
        * gdb/ui-file.c (gdb_flush): Rename to...
        (ui_file_flush): ...this.
        (stderr_file::write): Update.
        (stderr_file::puts): Update.
        * gdb/ui-file.h (gdb_flush): Rename to...
        (ui_file_flush): ...this.
        * gdb/utils.c (gdb_flush): Add function.
        * gdb/utils.h (gdb_flush): Add declaration.

Change-Id: I7ca143d30f03dc39f218f6e880eb9bca9e15af39