Update on descriptors

This PR improves the descriptors management.

• Fields computation is simplified and corrected in some corner cases
• Descriptor can now be given a name to improve debug/tracing information
• Tiles can also be individually named if CHAMELEON_KERNELS_TRACE cmake option is enabled
• core_ztile interface is updated to accept descriptor and print log calls (can be disable through environment variable CHAMELEON_COREBLAS_SILENT similarly to STARPU_SILENT)
• Recursive descriptors management is introduced as a first step toward recursive algorithm
• A CHAMELEON_Desc_Print function has been added to help debug the descriptor information (tile size, leading dimensions, ...)

Additionally:

• Fix a small issue with flush in starpu
• Silent warnings issued from the hmat merge
• Add the -Werror option to the CI build to avoid warnings
• Add a chameleon_ceil function to simplify computations in algorithms