fix build using Watcom :
./src/render/SDL_render.c(2168): Error! E1054: Expression must be constant
./src/render/SDL_render.c(2168): Error! E1054: Expression must be constant
./src/render/SDL_render.c(2175): Error! E1054: Expression must be constant
./src/render/SDL_render.c(2175): Error! E1054: Expression must be constant
./src/render/SDL_render.c(2322): Error! E1054: Expression must be constant
./src/render/SDL_render.c(2322): Error! E1054: Expression must be constant
./src/render/SDL_render.c(2322): Error! E1054: Expression must be constant
./src/render/SDL_render.c(2322): Error! E1054: Expression must be constant
./src/render/SDL_render.c(2329): Error! E1054: Expression must be constant
./src/render/SDL_render.c(2329): Error! E1054: Expression must be constant
./src/render/SDL_render.c(2329): Error! E1054: Expression must be constant
./src/render/SDL_render.c(2329): Error! E1054: Expression must be constant
./src/render/software/SDL_render_sw.c(602): Error! E1054: Expression must be constant
./src/render/software/SDL_render_sw.c(602): Error! E1054: Expression must be constant
./src/render/software/SDL_render_sw.c(602): Error! E1054: Expression must be constant
./src/render/software/SDL_render_sw.c(602): Error! E1054: Expression must be constant
2 files changed
