ReconstructionDataFormats: place the Vertex and HelixHelper constants in the constant address space

MSL requires every variable at program scope, class-scope statics included, to
name an address space. GPUglobalconstexpr() expands to constexpr everywhere
except Metal, so this is a no-op for host, CUDA, HIP, OpenCL and cling.

These were missed by the earlier pass: the header they sit in only started
being compiled once the errors ahead of it were gone.

Author: ktf

DataFormats/Reconstruction/include/ReconstructionDataFormats/HelixHelper.h

@@ -54,7 +54,7 @@ struct TrackAuxPar : public o2::math_utils::CircleXYf_t {
 //__________________________________________________________
 //< crossing coordinates of 2 circles
 struct CrossInfo {
-  static constexpr float MaxDistXYDef = 10.;
+  static GPUglobalconstexpr() float MaxDistXYDef = 10.;
   float xDCA[2] = {};
   float yDCA[2] = {};
   int nDCA = 0;

DataFormats/Reconstruction/include/ReconstructionDataFormats/Vertex.h

@@ -42,7 +42,7 @@ class VertexBase
                         kCovXZ,
                         kCovYZ,
                         kCovZZ };
-  static constexpr int kNCov = 6;
+  static GPUglobalconstexpr() int kNCov = 6;
   GPUhdDefault() VertexBase() = default;
   GPUhdDefault() ~VertexBase() = default;
   GPUhd() VertexBase(const float* pos, const float* cov)