incdir.sh, incdir.bat, incdir.c

Different compilers have different conventions for specifying lists of include file paths on the compiler command line. This incdir.sh bash script allows the build system to create include file paths without concern for the particular compiler in use.

The incdir.bat script is a counterpart for use in the native Windows build. However, there is currently only one compiler supported in that context: MinGW-GCC.

incdir.c is a higher performance version of incdir.sh, converted to C.