Run ssl-opt.sh on config-mini-tls1_1.h

[gilles-peskine-arm]

Since #5730, we run ssl-opt.sh on config-ccm-psk-dtls1_2.h, config-suite-b.h and config-thread.h. A lot of test cases don't run because they rely on features that aren't present in the particular configuration, but it's a start.

The goal of this task is to run ssl-opt.sh on config-mini-tls1_1.h. For test cases that cannot run in that configuration, ensure there are proper explicit or automatic requires_xxx instructions to skip those test cases. For test cases that can run, they should pass, and if not fixing bugs is part of the task. Build on the work I've already done — see below.

config-mini-tls1_1.h only exists in 2.28. However, I expect that some of the automation added to detect requirements in ssl-opt.sh is also useful in development and forward-porting that is part of the task.

Difficulty estimate: this is a continuation of #5582 and its 2.28 backport #5730. That one started as S but the backport made it overflow into M. I've already made a significant headway into 1.1, however, so I think what remains to be done is more of an S. My work in progress is at https://github.com/gilles-peskine-arm/mbedtls/tree/ssl-opt-mini-tls1_1-2.28-1. Some commits are already in #5730, the others need to be cherry-picked onto mbedtls-2.28 after #5730 is merged.