GPUUtils: place shared 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.

Author: ktf

GPU/Utils/GPUCommonBitSet.h

@@ -42,7 +42,7 @@ class bitset
   GPUdDefault() constexpr bitset(const __constant bitset&) = default;
 #endif // __OPENCL__
   GPUd() constexpr bitset(uint32_t vv) : v(vv) {};
-  static constexpr uint32_t full_set = ((1ul << N) - 1ul);
+  static GPUglobalconstexpr() uint32_t full_set = ((1ul << N) - 1ul);
 
   GPUd() constexpr bool all() const { return (v & full_set) == full_set; }
   GPUd() constexpr bool any() const { return v & full_set; }

GPU/Utils/MultivariatePolynomialHelper.h

@@ -163,8 +163,8 @@ class MultivariatePolynomialParametersHelper
 template <uint32_t Dim, uint32_t Degree, bool InteractionOnly>
 class MultivariatePolynomialHelper : public MultivariatePolynomialParametersHelper
 {
-  static constexpr uint16_t FMaxdim = 10;   ///< maximum dimensionality of the polynomials (number of different digits: 0,1,2,3....9 )
-  static constexpr uint16_t FMaxdegree = 9; ///< maximum degree of the polynomials (maximum number of digits in unsigned integer - 1)
+  static GPUglobalconstexpr() uint16_t FMaxdim = 10;   ///< maximum dimensionality of the polynomials (number of different digits: 0,1,2,3....9 )
+  static GPUglobalconstexpr() uint16_t FMaxdegree = 9; ///< maximum degree of the polynomials (maximum number of digits in unsigned integer - 1)
 
 #if !defined(GPUCA_GPUCODE)
   static_assert(Dim <= MultivariatePolynomialHelper<Dim, Degree, InteractionOnly>::FMaxdim && Degree <= MultivariatePolynomialHelper<Dim, Degree, InteractionOnly>::FMaxdegree, "Max. number of dimensions or degrees exceeded!");