INSTALL: document shared library pinning for static builds

INSTALL: document shared library pinning for static builds

The libcrypto library uses shared library pinning to prevent its
cleanup handlers from crashing at program termination because of a
premature unloading of the shared library.

However, shared library pinning is enabled also for static builds,
which may lead to surpising behaviour if libcrypto is linked
statically to a shared third-party library, because in this case
the third-party library gets pinned.

This surprising behaviour is caused by the fact that the `no-shared`
configure option does not imply `no-pinshared`. Since this quirk
can't be changed without potentially breaking existing code, we just
document it here and provide a workaround.

Fixes #20977

Reviewed-by: Todd Short <todd.short@me.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20985)