This is implemented for gint only currently; on Vhex, _Exit() is likely
just going to be a syscall. For CASIOWIN, this is slightly more
difficult, as there is no native exit syscall.
On sh-generic targets, the headers <bits/cpucap.h> (in C) and
<bits/asm/cpucap.h> (in assembler) provide definitions to acces the
__cpucap symbol which provides information on the CPU.
Currently, a single capability __CPUCAP_SH4ALDSP is defined; it
represents the SH4 extended instructions together with the integrated
DSP instructions. The main uses of this capability are [movua.l]
(unaligned reads) and [ldrc] (built-in tight loops).
Capabilities are initialized to 0 (their safest default) and the runtime
can enable them based on what hardware is running.
