Simplify and speed up numeric comparisons

Simplify and speed up numeric comparisons

This makes comparison functions (=, /=, <, <=, >, >=, min, max) quite
a bit faster (10-20 %).  Bytecode ops on fixnums are not affected,
nor is `value<`.

* src/data.c (arithcompare): Simplify the code to reduce the number of
branches.  Remove the comparison code argument; instead, return the
relation encoded as bits, which can be tested cheaply.  All callers
adapted.
* src/lisp.h (enum Arith_Comparison): Remove.
(Cmp_Bit_*, cmp_bits_t): New.

(cherry picked from commit 2fd38e5c496a2351a25e95df37a7900f6f80f22f)