Refactor the computation of API version limits

Previously, the API version limit was indicated with a numeric version
number.  This was "natural" in the pre-3.0.0 because the version was
this simple number.

With 3.0.0, the version is divided into three separate numbers, and
it's only the major number that counts, but we still need to be able
to support pre-3.0.0 version limits.

Therefore, we allow OPENSSL_API_COMPAT to be defined with a pre-3.0.0
style numeric version number or with a simple major number, i.e. can
be defined like this for any application:

    -D OPENSSL_API_COMPAT=0x10100000L
    -D OPENSSL_API_COMPAT=3

Since the pre-3.0.0 numerical version numbers are high, it's easy to
distinguish between a simple major number and a pre-3.0.0 numerical
version number and to thereby support both forms at the same time.

Internally, we define the following macros depending on the value of
OPENSSL_API_COMPAT:

    OPENSSL_API_0_9_8
    OPENSSL_API_1_0_0
    OPENSSL_API_1_1_0
    OPENSSL_API_3

They indicate that functions marked for deprecation in the
corresponding major release shall not be built if defined.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7724)