MAKEALL: Add summary information

This change adds some basic summary information to the MAKEALL script.
The summary information includes how many boards were compiled, how many
boards had compile warnings or errors, and which specific boards had
compile warnings or errors.

This information is useful when doing compile testing to quickly
determine which boards are broken.

As a side benefit, no empty $BOARD.ERR files are generated by MAKEALL.
Previously, each board had a corresponding $BOARD.ERR file, even if the
board compiled cleanly.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>