Suport passing arbitrary llvm arguments (#271)

- Support for passing LLVM command line options via the prcoess input or
providing one or more `--llvm-arg='..'` resolc CLI flag. This allows
more fine-grained control over the LLVM backend configuration.
- Make LLVM initialization idempotent.

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

crates/llvm-context/Cargo.toml

@@ -22,6 +22,7 @@ num = { workspace = true }
 hex = { workspace = true }
 sha3 = { workspace = true }
 inkwell = { workspace = true }
+libc = { workspace = true }
 polkavm-disassembler = { workspace = true }
 polkavm-common = { workspace = true }