Include the fallback sources in the build, and update
src/Makefile.sources so that it can be read by the CMake build files.
Fix a typo in the DirectWrite configure option so that we can properly
enable DirectWrite builds.
Also, when building the utility program, install them as well.
The 'avar' table does not allow random access to axis maps,
so change API to avoid quadratic-time implementation.
Removed -hb_ot_var_normalize_axis_value(), added
+hb_ot_var_normalize_variations() and
+hb_ot_var_normalize_coords() instead.
This moves all the source listings in src/Makefile.am,
src/hb-ucdn/Makefile.am and util/Makefile.am into separate Makefile
snippets, so that they may be shared between different Makefile-based
build systems, such as NMake for Visual Studio.