Add an option to build a static library

[qikp0]

Closes #241

I've tested it with the built-in tests, with a modified CPPFLAGS. It does still function and hardened_malloc is in use.

It appears to automatically build it by default.

[qikp0]

@thestinger any updates?

[thestinger]

@charles25565 Please rebase it instead of merging. You can just rebase it on top of main and it will drop the merge.

[qikp0]

@charles25565 Please rebase it instead of merging. You can just rebase it on top of main and it will drop the merge.

Figured that out.

Just sync the fork using whichever method, then clone, then switch to the branch, then rebase to main, then force push.

[qikp0]

The GrapheneOS team has told me that this feature is low priority and they have a bunch of other tasks to do other than random tiny features that don't improve security, such as this PR.

If you are a user and wondering why this PR hasn't been merged yet, this is why.

If you really need it for a project you can manually merge the PR yourself to your local hardened_malloc tree.