p11-kit: Expose version information through macros

[ueno]

This provides P11_KIT_VERSION_{MAJOR,MINOR,MICRO} from the <p11-kit/version.h> header, along with a helper macro P11_KIT_CHECK_VERSION(major, minor, micro) for checking the version requirement with #if directive.

Fixes: #523

[coveralls]

coverage: 69.556% (+0.001%) from 69.555%
when pulling fda7039 on ueno:wip/dueno/version-api
into 8832556 on p11-glue:master.

[ZoltanFridrich]

Looks good.

[ueno]

Thanks for the review!

[bcsgh]

Why is P11_KIT_CHECK_VERSION a macro rather than a function? That kind of removes one of the reason for including this sort of API which is to check at runtime that the library linked in (either linked statically at build time or dynamically from whatever environment things are run in) matches the expectation of the calling code. This macro at most allows calling code the verify that the set of headers resolved at build time are the expected ones but doesn't, by itself, provide a way to know what version of the p11 library the code is then linked with.

Given that p11 seems to require non-static builds, it seems like being able to verify that the (unavoidable) .so that is chosen at run time is what the calling code expects it to be (or at least having a way to know what it actually is) would be at least as desirable here as it is for other libraries that provide that sort of function:

• Asn1 asn1_check_version
• IDN2 idn2_check_version
• Nettle nettle_version_major/nettle_version_minor
• Curl curl_version_info
• Enki ev_version_major/ev_version_mnor
• Lua lua_version
• And others (those are just the ones I found in a few minutes in code I wrote).

[ueno]

I actually thought that run-time detection was already possible through PKCS#11 API (because libp11-kit.so is the same binary as p11-kit-proxy.so), but it turns out not the case. Maybe we could embed the actual version.