WIP: I started trying to build gtkplus@3.20, but this package has many more
dependencies than v2 and it requires newer versions of existing packages. This
commit provides updates for 5 packages that are required by GTK+3. This is not
the complete set of changes required for GTK+3.
atk - move default version from 2.14 -> 2.20.
glib - move default version from 2.42 -> 2.49
- v2.49 requires pcre+utf as a new dependency.
pcre - if variant +utf is selected, add '--enable-unicode-properties' to the
configure options.
libepoxy - new package to spack
- manages OpenGL function pointers.
pango - move default version from 1.36 -> 1.40
