The problem arose because we were setting LL_COMMON_BUILD in
llcommon/CMakeLists.txt, not only for the library build itself but also for
its LL_ADD_INTEGRATION_TEST tests. This told all the headers compiled into the
INTEGRATION_TEST_lllazy executable that the executable was providing all the
llcommon symbols, rather than importing them.
The solution is to switch to the llcommon_EXPORTS symbol automagically defined
by CMake when building the llcommon shared library itself.