Correct set_source_files_properties usage

Correct set_source_files_properties usage

The use of `CMAKE_BINARY_DIR` and `CMAKE_CURRENT_BINARY_DIR` when
specifying files to set_source_files_properties caused problems
when this project is used from another CMake project.

More specifically, these variables aren't set to the expected path,
and the properties are attempted to be set for non-existant files.

This was benign before vectorscan 5.4.8 as the only properties
set were warning suppression flags.

Starting with 5.4.9, `-funsigned-char` was applied to Ragel outputs
using this method. The result is projects depending on Vectorscan
through Cmake do not have this compile flag properly applied.