This patch takes the next step towards migrating all of DynamoRIO's context switching to support AVX-512. The function proc_num_simd_saved_abs() is introduced that returns the total number of SIMD registers on a given processor and OS. In the future, this number may be different from proc_num_simd_saved() that returns the number of SIMD registers that are actually saved by DynamoRIO and may be optimized. MCXT_NUM_SIMD_SLOTS is now the static number of slots in DynamoRIO's mcontext, regardless of what processor and OS actually support.
Issue: #1312