md-x86-gcc/support.c: fix omitted variable declaration

it's quite strange that this didnt cause a build error before...
fix INLINE related breakage from new dms C files

short version: inline on its own doesn't make sense - how can
you export a function and at the same time inline it ?

thus use static inline.
also reorder the code so the bogus forward declarations are not
needed anymore.
add build script for linux with sdl-gui
Merge pull request #39 from rofl0r/fix270b8

fixes 270b8, from rofl0r