openssl: fix the data race when sharing an SSL session between threads

The SSL_Session object is mutated during connection inside openssl,
and it might not be thread-safe. Besides, according to documentation
of openssl:

```
SSL_SESSION objects keep internal link information about the session
cache list, when being inserted into one SSL_CTX object's session
cache. One SSL_SESSION object, regardless of its reference count,
must therefore only be used with one SSL_CTX object (and the SSL
objects created from this SSL_CTX object).
```
If I understand correctly, it is not safe to share it even in a
single thread.

Instead, serialize the SSL_SESSION before adding it to the cache,
and deserialize it after retrieving it from the cache, so that no
concurrent write to the same object is infeasible.

Also
 - add a ci test for thread sanitizer
 - add a test for sharing ssl sessions concurrently
 - avoid redefining memory functions when not building libcurl, but
   including the soruce in libtest
 - increase the concurrent connections limit in sws

Notice that there are fix for a global data race for openssl which
is not yet release. The fix is cherry pick for the ci test with
thread sanitizer.
d8def79838

Closes #14751

tests/data/Makefile.am

@@ -268,6 +268,6 @@ test3024 test3025 test3026 test3027 test3028 test3029 test3030 \
 \
 test3100 test3101 test3102 test3103 \
 test3200 \
-test3201 test3202 test3203 test3204 test3205
+test3201 test3202 test3203 test3204 test3205 test3207
 
 EXTRA_DIST = $(TESTCASES) DISABLED