Remove llvm patch

[lrettig]

Closes #6

Wait until athenavm/athena#91 has been merged, then merge this and cut a release

[lrettig]

This still needs some work. It's working well on Linux, but I'm still having problems on Mac, which I thought were addressed. The clang that's installed out of the box on Ubuntu seems to feature RISC-V support, but this isn't the case on macOS and I'm having trouble compiling a compatible version of llvm/clang, especially on Apple Silicon. One reason is this obnoxious libc bug. Also, the riscv-gnu-toolchain isn't well supported on Apple Silicon yet (riscv-collab/riscv-gnu-toolchain#1445, riscv-collab/riscv-gnu-toolchain#1483).

I still think I can work around this but it'll take more time.

Ubuntu:

> uname -a
Linux 5.15.0-118-generic #128-Ubuntu SMP Fri Jul 5 09:28:59 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux
> cat /etc/os-release
PRETTY_NAME="Ubuntu 22.04.4 LTS"
> which clang
/usr/bin/clang
> clang -v
Ubuntu clang version 14.0.0-1ubuntu1.1
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/11
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/12
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/12
Candidate multilib: .;@m64
Selected multilib: .;@m64
Found CUDA installation: /usr/local/cuda-11.8, version
> clang --print-targets | grep -i riscv
    riscv32    - 32-bit RISC-V
    riscv64    - 64-bit RISC-V

macOS 14.6 on Apple Silicon:

% uname -a
Darwin 23.6.0 Darwin Kernel Version 23.6.0: Mon Jul 29 21:13:04 PDT 2024; root:xnu-10063.141.2~1/RELEASE_ARM64_T6020 arm64
% sw_vers
ProductName:            macOS
ProductVersion:         14.6.1
BuildVersion:           23G93
% which clang
/usr/bin/clang
% clang -v
Apple clang version 15.0.0 (clang-1500.3.9.4)
Target: arm64-apple-darwin23.6.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin
% clang -print-targets | grep -i riscv
%