Impala's toolchain builds Kudu using its toolchain compiler and libraries. The compiler and options are set in the standard environment variables CC, CXX, etc., but the boost build results in the system compiler being used. However, the CFLAGS/CXXFLAGS do get picked up, so the combination is not guaranteed to be supported, and Impala toolchain builds do end up failing.
I believe the project-config.jam needs to be set for boost to pick up the right compiler. It is only being set for *san builds currently (to use clang).