how to get trunk revision in the gcc configuration output?

[IainS <developer@xxxxxxxxxxxxxxxxxxxxxx>]

Hi,

A dumb question...

I notice that many people produce test results with  compiler  
identifiers of the form:

...../ xgcc  version 4.5.0 20090424 (experimental) [trunk revision  
146740] (GCC)

What is the incantation to get the [trunk revision xxxxxx] part  
included?

googling / searching the gcc list  with the subject question yielded  
no info...

cheers,
Iain