gplugin/gplugin

Both tcc/ and vala/ were also referencing meson.build_root
feature/meson-subproject-fix
2019-08-12, Gary Kramlich
6354bdbff214
Both tcc/ and vala/ were also referencing meson.build_root
export GPLUGIN_VERSION=@GPLUGIN_MAJOR_VERSION@.@GPLUGIN_MINOR_VERSION@.@GPLUGIN_MICRO_VERSION@