The ACLE defines a feature macro called __ARM_ACLE:

__ARM_ACLE is defined to the version of this specification implemented,
as 100 * major_version + minor_version. An implementation implementing
version 2.1 of the ACLE specification will define __ARM_ACLE as 201.

However, a long time ago, we changed the versioning scheme of the ACLE
from "major.minor" to a combination of year and quarter. For instance
the latest release is 2023 Q2.

Since the macro's definition is now out of date, we now move to a new
scheme:

`__ARM_ACLE` is defined to the version of this specification implemented,
formatted as `{YEAR}{QUARTER}{PATCH}`.

The value would be the integer formed by the year (4 digits)
concatenated to the quarter's number (1 digit), finally concatenated to
the patch release (1 digit). So the macro's value for the 2023 Q2
release with no patch release would then be 202320. Using 4 digits for
the year, and having it preceding the quarter, will be helpful to
ensure the formed integer values will be greater than the ones using the
previous/current format.