This copy of uniwidth is a modified subset of gnulib.

commit c8e351542405558d06af899761b30c3db6409486
math: More clang -Winclude-next-absolute-path silencing.

The following changes have been made to the original:

- Only the uniwidth subset is included.

- A CMake build system has been added.

- .in.h files have been changed to .h.

- CJK encoding checks have been removed, since we're only
  using UTF-8.

To obtain the original gnulib, visit:
https://www.gnu.org/software/gnulib/
