I found cause of my problem with building libc6-dev package on Jessie.

Code is invoked in following, simplified order

1. $ git buildpackage
2. code compilation
3. pbuilder invocation
4. package building in pbuilder environment

It should be obvious, but neither I noticed nor I thought that it is done that way.

Currently I’m examining if it will be possible to change order of steps to:

1. $ git buildpackage
2. pbuilder invocation
3. code compilation in pbuilder environment
4. package building in pbuilder environment