In general "\%s" doesn't seem to be a valid printf format specifier. Given where it originally came from and how OneLine() is used elsewhere I'm pretty sure that it should rather read "%s".
If an Amiga specific spawnvp() is the only alternative it seems save to classify the UNIX specific spawnvp() as default.
Added projects for the remaining binaries to the MS VS 2010 solution.
Allow to supply searchpath defines as simple values instead of escaped C strings.
Replaced whole bunch for Makefiles with a single generic Makefile.

- Targeting GNU toolchain.
- Modern dependency handling.
- Warning-free build.
- GCC option -Werror set.
- Dynamic search paths.
- Don't write into source directories.
- Easy cleanup by just removing 'wrk'.