[PING^2] PR 23572 warnings for out of range floating-point constants

[Manuel López-Ibáñez]

The patch was rejected, as it is here
http://gcc.gnu.org/ml/gcc-patches/2007-01/msg01730.html
However, the conversation ended abruptly here
http://gcc.gnu.org/ml/gcc-patches/2007-01/msg01752.html
without specifying what the correct fix (if any) would be.
If no fix is possible, we should close PR 23572.

My proposal:

* Warning for overflow is pedwarn if infinities are not supported.

* If infinities are supported, warn for overflow with Woverflow.

* warn for underflow with Woverflow (so we don't have to introduce a
Wunderflow switch just for this).

I think this will be enough to close PR 23572.

Does this seem OK?

Cheers,

Manuel.