configure: rationalise error messages with meaningful texts

Currently, error messages just state the obvious: a required
component is required. While in some cases, there is not much
else to say, in some other cases we could tell much more.

For example, a missing libstdc++ means no static toolchain.

Also, format error and warning messages in a similar fashion,
with a {error,warning} intro, followed by the message specified
by the caller.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

This is NOT the official version of dialog.  This version has been

significantly modified from the original.  It is for use by the Linux

kernel configuration script.  Please do not bother Savio Lam with 

questions about this program.