Fix android static link libstdcxx for mtmd

[AsbjornOlling]

I recently added #947
but it has a bad interaction with the mtmd feature added in #938

The mtmd build stuff doesn't respect the static stdcxx stuff.

I'm leaving this as draft until I've tested it on my project downstream, but it should be correct.

[AsbjornOlling]

Whoops, accidentally had some unrelated commits on the same branch. Cleaned it up and force pushed.

[AsbjornOlling]

Also bumped llama.cpp submodule to the latest tagged build.

The version currently on main has a bug that breaks all windows builds. On my project we pinned this crate to one of the nightly branches of this repo precisely to get the fix for that bug (which has been upstreamed for a little while in llama.cpp).

When I was building and running my test suites on my project using this PR branch, I hit a bunch of windows failures. Hence the submodule bump.

[MarcusDunn]

lgtm. when this isn't a draft and CI passes I will merge

[MarcusDunn]

conflict with #952 I think, I'll take whichever is newer.

[AsbjornOlling]

The llama.cpp commit on this branch is newer - b8310 here vs b8233 on #952

[MarcusDunn]

could you take yous in the merge? will merge once that's done.

[AsbjornOlling]

@MarcusDunn rebased on main.