Could we get a LP64 version identifier?

[Walter Bright]

Frits van Bommel wrote:
> Some testing shows that all DMD-frontend based compilers (i.e. DMD, GDC 
> and LDC) seem to produce that error message for any version identifier 
> starting with "D_" (Including "D_" itself).

The point of that is to ensure that the D_ name space is reserved for 
predefined version identifiers. This check is done in 
VersionCondition::checkPredefined() in cond.c.