After reinstatement of DSO support in APR/APR-util, revert r1837437, r1837435, r1834553, r1833598, r1833452, r1833383, r1833368.
Undoes the following:
mod_ssl: OpenSSL now initializes fully through APR, use that.
mod_ssl: build with LibreSSL.
LibreSSL seems to be openssl-1.1 API compatible only in version 2.8 (master). So use that for MODSSL_USE_OPENSSL_PRE_1_1_API instead of 2.7, the two 2.7 compatibility-exceptions are handled explicitely but overall it's simpler.
Regarding CRYPTO_malloc_init vs OPENSSL_malloc_init, libreSSL uses none, the former used to be a no-op but depends is LIBRESSL_INTERNAL in latest versions, while the latter has never been (and will never be) defined. So don't call any with LibreSSL.
Follow up to r1833368: share openssl between modules.
Both libapr[-util], the core PRNG, mod_ssl, mod_crypto and mod_session_crypto can use the same crypto library (e.g. openssl), use the new APR crypto loading API so that they can work together and initialize/terminate the lib either once for all or on demand and reusable by the others.
Follow up to r1833368: apr_crypto_prng_after_fork() now used a PID.
Make use of the new apr_crypto_rng API if available.