[SYCL][COMPAT] Add bfloat16 support to several maths ops (#15572)

Adds support for `sycl::ext::oneapi::bfloat16` to:
 - `relu`
 - `clamp`
 - `fmax_nan`
 - `fmin_nan`
 - `min`
 - `max`
 - `compare_mask`
 - `unordered_compare_mask`

sycl/doc/syclcompat/README.md

@@ -1729,7 +1729,51 @@ second operand, respectively. These three APIs return a single 32-bit value with
 the accumulated result, which is unsigned if both operands are `uint32_t` and
 signed otherwise.
 
+Various maths functions are defined operate on any floating point types.
+`syclcompat::is_floating_point_v` extends the standard library's
+`std::is_floating_point_v` to include `sycl::half` and, where available,
+`sycl::ext::oneapi::bfloat16`. The current version of SYCLcompat also provides
+a specialization of `std::common_type_t` for `sycl::ext::oneapi::bfloat16`,
+though this will be moved to the `sycl_ext_oneapi_bfloat16` extension in
+future.
+
+```cpp
+namespace std {
+template <> struct common_type<sycl::ext::oneapi::bfloat16> {
+  using type = sycl::ext::oneapi::bfloat16;
+};
+
+template <>
+struct common_type<sycl::ext::oneapi::bfloat16, sycl::ext::oneapi::bfloat16> {
+  using type = sycl::ext::oneapi::bfloat16;
+};
+
+template <typename T> struct common_type<sycl::ext::oneapi::bfloat16, T> {
+  using type = sycl::ext::oneapi::bfloat16;
+};
+
+template <typename T> struct common_type<T, sycl::ext::oneapi::bfloat16> {
+  using type = sycl::ext::oneapi::bfloat16;
+};
+} // namespace std
+```
+
 ```cpp
+namespace syclcompat{
+
+// Trait for extended floating point definition
+template <typename T>
+struct is_floating_point : std::is_floating_point<T>{};
+
+template <> struct is_floating_point<sycl::half> : std::true_type {};
+
+#ifdef SYCL_EXT_ONEAPI_BFLOAT16_MATH_FUNCTIONS
+template <> struct is_floating_point<sycl::ext::oneapi::bfloat16> : std::true_type {};
+#endif
+template <typename T>
+
+inline constexpr bool is_floating_point_v = is_floating_point<T>::value;
+
 inline unsigned int funnelshift_l(unsigned int low, unsigned int high,
                                   unsigned int shift); 
 
@@ -1756,11 +1800,9 @@ inline std::enable_if_t<ValueT::size() == 2, ValueT> isnan(const ValueT a);
 // cbrt function wrapper.
 template <typename ValueT>
 inline std::enable_if_t<std::is_floating_point_v<ValueT> ||
-                            std::is_same_v<sycl::half, ValueT>,
+                            std::is_same_v<ValueT, sycl::half>,
                         ValueT>
-cbrt(ValueT val) {
-  return sycl::cbrt(static_cast<ValueT>(val));
-}
+cbrt(ValueT val);
 
 // For floating-point types, `float` or `double` arguments are acceptable.
 // For integer types, `std::uint32_t`, `std::int32_t`, `std::uint64_t` or
@@ -1798,6 +1840,10 @@ template <typename ValueT, typename ValueU>
 inline sycl::vec<std::common_type_t<ValueT, ValueU>, 2>
 fmax_nan(const sycl::vec<ValueT, 2> a, const sycl::vec<ValueU, 2> b);
 
+template <typename ValueT, typename ValueU>
+inline sycl::marray<std::common_type_t<ValueT, ValueU>, 2>
+fmax_nan(const sycl::marray<ValueT, 2> a, const sycl::marray<ValueU, 2> b);
+
 // Performs 2 elements comparison and returns the smaller one. If either of
 // inputs is NaN, then return NaN.
 template <typename ValueT, typename ValueU>
@@ -1807,6 +1853,10 @@ template <typename ValueT, typename ValueU>
 inline sycl::vec<std::common_type_t<ValueT, ValueU>, 2>
 fmin_nan(const sycl::vec<ValueT, 2> a, const sycl::vec<ValueU, 2> b);
 
+template <typename ValueT, typename ValueU>
+inline sycl::marray<std::common_type_t<ValueT, ValueU>, 2>
+fmin_nan(const sycl::marray<ValueT, 2> a, const sycl::marray<ValueU, 2> b);
+
 inline float pow(const float a, const int b) { return sycl::pown(a, b); }
 inline double pow(const double a, const int b) { return sycl::pown(a, b); }
 
@@ -1867,14 +1917,13 @@ unordered_compare_both(const ValueT a, const ValueT b,
                        const BinaryOperation binary_op);
 
 template <typename ValueT, class BinaryOperation>
-inline unsigned compare_mask(const sycl::vec<ValueT, 2> a,
-                             const sycl::vec<ValueT, 2> b,
-                             const BinaryOperation binary_op);
+inline std::enable_if_t<ValueT::size() == 2, unsigned>
+compare_mask(const ValueT a, const ValueT b, const BinaryOperation binary_op);
 
 template <typename ValueT, class BinaryOperation>
-inline unsigned unordered_compare_mask(const sycl::vec<ValueT, 2> a,
-                                       const sycl::vec<ValueT, 2> b,
-                                       const BinaryOperation binary_op);
+inline std::enable_if_t<ValueT::size() == 2, unsigned>
+unordered_compare_mask(const ValueT a, const ValueT b,
+                       const BinaryOperation binary_op);
 
 template <typename S, typename T> inline T vectorized_max(T a, T b);
 
@@ -1928,6 +1977,7 @@ inline dot_product_acc_t<T1, T2> dp2a_hi(T1 a, T2 b,
 template <typename T1, typename T2>
 inline dot_product_acc_t<T1, T2> dp4a(T1 a, T2 b,
                                       dot_product_acc_t<T1, T2> c);
+} // namespace syclcompat
 ```
 
 `vectorized_binary` computes the `BinaryOperation` for two operands,