re-enable the fix for broken friction in Clang (got accidently undone in a recent commit)

fix OSX build

src/BulletDynamics/ConstraintSolver/btSequentialImpulseConstraintSolver.cpp

@@ -606,8 +606,8 @@ void btSequentialImpulseConstraintSolver::setupFrictionConstraint(btSolverConstr
 
 //		btScalar positionalError = 0.f;
 
-		btSimdScalar velocityError =  desiredVelocity - rel_vel;
-		btSimdScalar	velocityImpulse = velocityError * btSimdScalar(solverConstraint.m_jacDiagABInv);
+		btScalar velocityError =  desiredVelocity - rel_vel;
+		btScalar velocityImpulse = velocityError * solverConstraint.m_jacDiagABInv;
 		solverConstraint.m_rhs = velocityImpulse;
 		solverConstraint.m_rhsPenetration = 0.f;
 		solverConstraint.m_cfm = cfmSlip;

src/LinearMath/btCpuFeatureUtility.h

@@ -5,9 +5,12 @@
 #include "LinearMath/btScalar.h"
 
 #include <string.h>//memset
-#ifdef  BT_USE_SSE
+#ifdef  USE_SIMD
+#include <emmintrin.h>
+#ifdef BT_ALLOW_SSE4
 #include <intrin.h>
-#endif
+#endif //BT_ALLOW_SSE4
+#endif //USE_SIMD
 
 #if defined BT_USE_NEON
 #define ARM_NEON_GCC_COMPATIBILITY  1