Add gc_mat4_imul prototype in gc_math.h.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Fix bug that caused triangle to not appear.

The ID matrix was changed from a static global variable to a function
call last week.  The memcpy was moving the function pointer into the
drawable's model transform matrix, which would have been complete
garbage.  But gcc doesn't care what type of void pointer it copies!

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Rotate the triangle by 0.01 degrees before it's drawn.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>