CL_M_* constants unspecified

The XML registry defines a number of math constants named `CL_M_*`. These are provided by `cl_platform.h` but are not described in any of the specifications.

Start by comparing the CL_M_* constants in the XML registry with their definitions in cl_platform.h, then identify which specifications omit their descriptions. Document the missing constants in the relevant specifications and verify that every registry constant is covered.

Written by the indexing model from the issue text.