main: sanity check cpu support
main: sanity check cpu support

We require SSE 4.2 (for commitlog CRC32), verify it exists early and bail
out if it does not.

We need to check early, because the compiler may use newer instructions
in the generated code; the earlier we check, the lower the probability
we hit an undefined opcode exception.

Message-Id: <57cab62e601122949c5884fd773e88173137c919@scylladb.com>

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