tests/lib: define _TP_COMPILATION for the internal variant
tests/lib: define _TP_COMPILATION for the internal variant

foo_CPPFLAGS overrides AM_CPPFLAGS, so if you want to include the latter
in the former, you have to do it explicitly.

Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib