Here's a patch for GPRbuild. Once xmlada-static is in place, it seems that setting XMLADA_BUILD to "static" is all that's needed when building GPRbuild.
It's still linked dynamically to GlibC, but I think that's OK. Soname changes in GlibC are extremely rare, and if it would happen, then it seems to me that a transition period with a compatibility package would be necessary.
Merry Christmas!
Björn