Add support for unexported variables access in live patches

[inconstante]

Read the commit message for more information...

Apart from that, the patch adds new information to the live patch metadata, more specifically, the addresses (offsets from the load address) of data objects, and that means that there is no need to open in-disk files (DSOs) during live patch application to fix references to LOCAL objects.

We should probably copy this mechanism to the other parts of the live patch metadata, so that, in the future, nothing else depends on the target library file being both in-disk and in the exact same version that the target process used (which doesn´t work after package updates).

[inconstante]

Commit b45f0f3 disabled optimization in the live patch, otherwise the reference variable disappears.

[inconstante]

Commit d40122a changes the following:

• undo the pragma optimize trick, which only worked with GCC;
• make sure that the reference var is not optimized away or placed into read-only sections by writing to it;
• fix coding-style issues pointed-out by the CI;
• fix make distcheck errors;
• describe the changes to the metadata description file in the manpages and in the README file.

Sorry for flooding the pull request with commits. :B

[inconstante]

Updated branch against current master.