Repair mismatched cmake _LIBRAR{Y,IES} variable.
Repair mismatched cmake _LIBRAR{Y,IES} variable.

This was breaking the build on Darwin. I don't know how it wasn't doing so on Linux
too; perhaps Linux triggers HAVE_ICONV_IN_LIBC so it never came up?

cmake wants all instances of this sort of variable to be named
> Xxx_LIBRARIES
>    The libraries to link against to use Xxx. These should include full paths. This should not be a cache entry.
- https://cmake.org/cmake/help/v3.0/manual/cmake-developer.7.html#find-modules

glassechidna/zxing-cpp,glassechidna/zxing-cpp