Workaround build failure on -fno-common toolchains like upstream
gcc-10. Otherwise build fails as:
ld: .libs/autodetection.o:/build/gtkpod-2.1.5/libgtkpod/gtkpod_app_iface.h:248: multiple definition of
`gtkpod_app'; .libs/gtkpod_app_iface.o:/build/gtkpod-2.1.5/libgtkpod/gtkpod_app_iface.h:248: first defined here