.a and .la in windows

How were the .a and .la files in the SDL-devel-1.2.4-mingw32.tar.gz
http://www.libsdl.org/release/SDL-devel-1.2.4-mingw32.tar.gz file
created? I need to create similar files for the SDL_mixer library.
Currently I have created an .a file for SDL_mixer from the SDL_mixer.dll
file using this method:
But when I compile anything when including SDL_mixer.h and linking with
SDL_mixer, I get tons of errors in the header file. All these come from
lines with SDL_mixer function prototypes on them.