PellesC IDE is coded using directly windows API, so there is no bloating code due to glue logic in large runtime libraries (C#, C++, etc.).
Most part of GUI and other functionalities are inside system DLL's (i.e. kernel32.lib, advapi32.lib, user32.lib, etc.) that are already loaded and shared with all programs (even those in C++ or C#, or any other HLL which always depends on the base API). They are simply linked with your C code.