Protect all SIMD implementations with the according defines and
let the compiler decide if it supports the intructions.
Linux will still use Simd_Generic because CPU feature runtime
detection is missing.
Get the idDrawVert member offsets directly instead of hardcoding
them and checking them via assert() at runtime.
Fixes compile error:
cast from pointer to smaller type 'int' loses information
variable set but not used
Removes some CollisionModel code under _DEBUG which was probably a
leftover, since it was completely useless (its done later anyways).
