If I read the manpage of pcreposix right, the (PCRE) regcomp function expects to be given P-regexes in all cases. Going with regex.h instead means regcomp will require B/E-regexes.

It's already bad enough that the (unmodified variant of the) software exhibits different behavior depending on which platform it was built, but now you're also changing the behavior within the context of one (fixated) platforms, which could, for example, invalidate the contents of configuration files that were written using the expectation that, on the openSUSE platform, sslh would always demand P-regexes. I would ask that you reconsider and drop the patch.