Use symbol versioning

[NWilson]

It is not possible to load two copies of PCRE2 into the same process address space, because we don't have versioned symbols. This would be an issue if an application links to one .so file with PCRE2, but then loads a component (a plugin perhaps) which is linked to a different .so containing PCRE2. The dynamic linker would not be able to resolve the symbols correctly to the two independent instances of the library.

We haven't had any user reports of issues, so I feel it's not urgent.

Raised in Debian bug 902060.