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x86/x64: Fix math.ceil(-0.9) result sign.

Reported by minoki.

(cherry-picked from commit 674afcd4e)

The `ceil` (`floor`) math function implementation calculates (|x| +
2^52) - 2^52 for its argument to determine the fractional part of x, so
it will be rounded to the nearest integer and its sign is restored.
After that, if the original value is < (>) than the result, the -1 (1)
is subtracted from it. Take a look at the `ceil()` case. The result of
the operation `-1 - (-1)` is +0 for FP arithmetic, against -0 expected
as a result.

This patch changes the `- (-1)` operation to `+ 1` and restores sign
after it again.

NB: Since in DUALNUM mode on x86/x64 all results are tried to be
converted to integers, the sign of 0 is neglected.

Sergey Kaplun:
* added the description and the test for the problem

Part of tarantool/tarantool#9145

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