[defectbydesign]

There are already "Name Spaces" in C and modules are actually object files or libraries.

You can spread components in as many object files or libraries as you wish.

IMHO it's not a C related problem but a code design one.

Write libraries (with headers) only if you need to share the code but if you're not sure about that just include it for your specific program.

There is no shame to include local files containing declarations and definitions.

I think it is a misconception from C programmers to write headers for local purpose.