Report a deprecation warning if UNSIGNED is used for FLOAT/DOUBLE/REAL
or DECIMAL columns.

This includes reporting warnings for CREATE TABLE ... LIKE
and CREATE TABLE ... SELECT which causes such columns to
be made.

Change-Id: Ia4229d4109f922ae59cfc7857aa9ae123228f5cb
(cherry picked from commit b6a8364b04560d81209aef08ffec4789f4ddf5e3)