message: guix: Build depends/qt with our platform definition
  Our 'bitcoin-linux-g++' definition better integrates with our depends
  system than the stock linux-g++-64 definition.
  This fixes a bug whereby Guix builds on x86_64 for x86_64 did not
  produce a QMinimalIntegrationPlugin and led to bitcoin-qt not being
  built.
diff: @@ -214,6 +214,7 @@ make -C depends --jobs="$JOBS" HOST="$HOST" \
  x86_64_linux_NM=x86_64-linux-gnu-nm \
  x86_64_linux_STRIP=x86_64-linux-gnu-strip \
  qt_config_opts_i686_linux='-platform linux-g++ -xplatform bitcoin-linux-g++' \
  + qt_config_opts_x86_64_linux='-platform linux-g++ -xplatform bitcoin-linux-g++' \
  FORCE_USE_SYSTEM_CLANG=1
  