[RFC] Change configure.in so -W arnings match reality

[Jim Kingdon]

> The attatched patch changes the default warnings used when compiling GDB
> so that they match the current reality (there are many more warnings
> that could be fixed but they are for post 5.0).

No objections but it doesn't solve the problem.  The defaults which
actually get used (on a vanilla "./configure && make") are in the
top-level configure (which is still using Cygnus configure not
autoconf) and are -W -Wall.  Since the top-level configure.in is
shared with other programs this isn't quite as easy (maybe it needs to
pass different values for each directory it recurses into?).