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Extend the CLibrary shared makefile to add support for building HAL and
kernel versions of libraries, with 'h' and 'k' suffixes respectively.
These are built with stack limit checking & frame pointers disabled, and
with RISCOS_HAL and RISCOS_KERNEL defines enabled as appropriate.

Note that currently there's nothing done to protect the SB register in
HAL builds of libraries, or to deal with references to data sections.