[SYCL] Hide new builtin definitions behind preview option (#11774)

The recently added builtin definitions were not part of the breaking
release, so to avoid API breaking changes for the next minor release
this patch reintroduces the old definition of builtins and hides the new
definitions behind the -fpreview-breaking-changes compiler option.

---------

Signed-off-by: Larsen, Steffen <[email protected]>

Author: steffenlarsen

sycl/include/sycl/builtins.hpp

@@ -10,11 +10,20 @@
 
 #include <sycl/detail/defines_elementary.hpp>
 
+#ifdef __INTEL_PREVIEW_BREAKING_CHANGES
+
 // Include the generated builtins.
 #include <sycl/builtins_marray_gen.hpp>
 #include <sycl/builtins_scalar_gen.hpp>
 #include <sycl/builtins_vector_gen.hpp>
 
+#else // __INTEL_PREVIEW_BREAKING_CHANGES
+
+#include <sycl/builtins_legacy_marray_vec.hpp>
+#include <sycl/builtins_legacy_scalar.hpp>
+
+#endif // __INTEL_PREVIEW_BREAKING_CHANGES
+
 #ifdef __SYCL_DEVICE_ONLY__
 extern "C" {