MINOR: debug: add the ability to enter components in the post_mortem struct

MINOR: debug: add the ability to enter components in the post_mortem struct

Here the idea is to collect components' versions and build options. The
main component is haproxy, but the API is made so that any sub-system
can easily add a component there (for example the detailed version of a
device detection lib, or some info about a lib loaded from Lua).

The elements are stored as a pointer to an array of structs and its count
so that it's sufficient to issue this in gdb to list them all at once:

  print *post_mortem.components@post_mortem.nb_components

For now we collect name, version, toolchain, toolchain options, build
options and path. Maybe more could be useful in the future.