Build most programs without OpenMP

As seen in https://github.com/openwall/john-packages/issues/723 and I've just confirmed on Linux, even separate program binaries like dmg2john get linked against OpenMP now. We should ideally avoid that, limiting such compiler/linker flags only to programs that actually use OpenMP.

I understand this can be tricky as some object files are shared between john and some *2john programs, and are built with OpenMP enabled even if unused, so theoretically could require the library at link time. It'd be extra effort for us to get them built with different compiler flags than the rest. It'd probably be less effort to omit OpenMP just at link time of *2john programs, hoping that no actual dependency got in despite of OpenMP enabled at compile time? Also, we somehow do avoid dependencies of *2john on most libraries that john uses, such as zlib and OpenSSL's libcrypto. So maybe not that hard to fix, after all?

Start by examining the build configuration and link commands for the separate *2john programs, then compare them with john's OpenMP-related flags. The issue is done when programs such as dmg2john no longer require OpenMP while john still links and builds with it; check the resulting binaries for their library dependencies.