Internal `malloc` and various improvements

[0152la]

Since this has quite a bit of changes, including lots of removals, I decided to open the PR as multiple commits, to make reviewing easier.

• Provide a malloc and friends compartment library to be used internally, overriding the previous interception implementation. We use the DDC capability to get the are of memory that is designated as heap space. This is done in a new library, libcomputils.so, to be loaded in a compartment. This means further libraries loaded will also use our own internal malloc implementation;
• Due to the above, now removed most of the intercept code; leftover code is meant to be rechecked and reworked at some point;
• Fix setting improper bounds for compartment DDC capabilities (i.e., ensure the capability encompasses only the memory region designated for a compartment), and now set the offset to match the start of the compartment heap, to use for internal malloc;
• Further improve symbol relocation lookup;
• Added a few more tests.

[ltratt]

Somehow I missed this one -- sorry!

[ltratt]

https://github.com/capablevms/CHERI-ELF-comp/pull/27/commits/bd730889c5f622ccedaf4ee0f2625732405dfc21 says "Remove some currently not working tests" but it adds two tests and removes none?

[0152la]

bd73088 says "Remove some currently not working tests" but it adds two tests and removes none?

I think I forgot to add CMakeLists.txt in that commit, and that got added in 06b708a.

[ltratt]

Please squash.

[0152la]

Squashed.

[ltratt]

@0152la I guess the new commit fixes things and this can be squashed? If so, please squash.

[0152la]

I wanted to do a bit further testing before going forward with this PR, in case anything else slipped through the cracks. I'll either squash it, or push further commits, based on how it goes.

[0152la]

Ready for review.

[ltratt]

Please squash.

[0152la]

Squashed.