abicompat: Add prompt message for abnormal operation

abicompat: Add prompt message for abnormal operation

When using abicompat, if the uses the --weak-mode option and also
provides a lib2 path on the command line, the lib2 path is silently
ignored.

This patch provides a warning to notify the user that the lib2 path is
ignored in that case.

	* tools/abicompat.cc (main): Notify the user when the path to
	the second library is ignored because the --weak-mode option
	was provided.  Also, fix comment.

Signed-off-by: tangmeng <tangmeng@uniontech.com>
Signed-off-by: Dodji Seketeli <dodji@redhat.com>