from wine repo cbe42036231a07d11f0ef6ba374d01aefa9b6a2c :
include math.h in d3dvec.inl as it uses sqrt().

git-svn-id: svn+ssh://svn.code.sf.net/p/mingw-w64/code/branches/releases/v1.0@4196 4407c894-4637-0410-b4f5-ada5f102cad1