GUB buiding from a local source tree?

[Boris Shingarov]

Hi,

How do I tell GUB to build Lilypond from a modified source tree which I 
have locally, instead of getting it from git?  In general, where is the 
best place to start reading more on GUB, the info on the GUB page is 
very sketchy, and GUB-related messages on lilypond-devel seem far apart 
and browsing the list archive for a while, did not get me very far. 
My immediate need is to test out my patches on the mingw platform.