message: Fix a warning in integration test / gmake / znc-buildmod interaction.
  It was requested on
diff: @@ -85,5 +85,10 @@ externalproject_add(inttest_bin
  "-DZNC_BIN_DIR:path=${CMAKE_INSTALL_FULL_BINDIR}"
  "-DQt5_HINTS:path=${brew_qt5}")
  add_custom_target(inttest COMMAND
  + # Prevent a warning from test of znc-buildmod, when inner make
  + # discovers that there is an outer make and tries to use it:
  + # gmake[4]: warning: jobserver unavailable: using -j1. Add '+' to parent make rule.
  + # This option doesn't affect ninja, which doesn't show that warning anyway.
  + ${CMAKE_COMMAND} -E env MAKEFLAGS=
  "${CMAKE_CURRENT_BINARY_DIR}/integration/inttest")
  add_dependencies(inttest inttest_bin)
  