feature request: compiler switch to output compiler defined version constants

[Steven Schveighoffer]

It would be nice if dmd -showversions output all the version constants 
defined by the compiler.  Why do I say this?  Because it's much more 
convenient than searching through the digital mars web site for predefined 
constants, then trying to figure out if those constants are defined or not 
by trying to compile a file with those version constants in it.  And this 
should be done in both D 1.0 and 2.0, as it doesn't affect the language.

BTW, if there is already some way to do this, please let me know :)

-Steve