Compilation warning fixes:

* new btSdfCollisionShapeInternalData() may not be allocated aligned 16
* Two cases of signed/unsigned mismatch

src/BulletCollision/CollisionShapes/btSdfCollisionShape.cpp

@@ -2,8 +2,11 @@
 #include "btMiniSDF.h"
 #include "LinearMath/btAabbUtil2.h"
 
-struct btSdfCollisionShapeInternalData
+ATTRIBUTE_ALIGNED16(struct)
+btSdfCollisionShapeInternalData
 {
+	BT_DECLARE_ALIGNED_ALLOCATOR();
+
 	btVector3 m_localScaling;
 	btScalar m_margin;
 	btMiniSDF m_sdf;

src/BulletDynamics/ConstraintSolver/btBatchedConstraints.cpp

@@ -852,7 +852,7 @@ static void setupSpatialGridBatchesMt(
 		memHelper.addChunk((void**)&constraintRowBatchIds, sizeof(int) * numConstraintRows);
 		size_t scratchSize = memHelper.getSizeToAllocate();
 		// if we need to reallocate
-		if (scratchMemory->capacity() < scratchSize)
+		if (static_cast<size_t>(scratchMemory->capacity()) < scratchSize)
 		{
 			// allocate 6.25% extra to avoid repeated reallocs
 			scratchMemory->reserve(scratchSize + scratchSize / 16);

src/LinearMath/btReducedVector.h

@@ -267,7 +267,7 @@ public:
         std::sort(tuples.begin(), tuples.end());
         btAlignedObjectArray<int> new_indices;
         btAlignedObjectArray<btVector3> new_vecs;
-        for (int i = 0; i < tuples.size(); ++i)
+        for (size_t i = 0; i < tuples.size(); ++i)
         {
             new_indices.push_back(tuples[i].b);
             new_vecs.push_back(m_vecs[tuples[i].a]);