[build2] libpq build failure

[Патрушев Данил Андреевич]

Yes, 'ibpq\version.' exactly. 

//build2 --version
build2 0.12.0-a.0.6e84c0f9c5e4
libbutl 0.12.0-a.0.b80818e87a57
host x86_64-w64-mingw32
Copyright (c) 2014-2019 Code Synthesis Ltd
This is free software released under the MIT license.

//msvc
Microsoft (R) C/C++ 19.16.27034  x64