meson.build always assumed running from git source tree,
resulting in GIT_VERSION with value "" (empty string).
This commit makes meson use the tarballed version.h,
for the cases when not building from git source tree.
when updating the ebuild i noticed that the include for the config.h and
version.h files relied on the build directory being name "build". This
is fixed now by using the last segment of the meson.build_root() output
which is the correct build dir.
also delete no longer needed manual creation of version.h and config.h
Nedko Arnaudov
Max Audron