Emerge Yul recompiler (#1)

Provide a modified (and incomplete) version of ZKSync zksolc that can compile the most basic contracts

crates/pallet-contracts-pvm-llapi/build.rs

@@ -0,0 +1,47 @@
+use std::{env, fs, path::Path, process::Command};
+
+fn compile(bitcode_path: &str) {
+    let output = Command::new("clang")
+        .args([
+            "--target=riscv32",
+            "-Xclang",
+            "-triple=riscv32-unknown-unknown-elf",
+            "-march=rv32em",
+            "-mabi=ilp32e",
+            "-fno-exceptions",
+            "-ffreestanding",
+            "-Wall",
+            "-fno-builtin",
+            "-O3",
+            "-emit-llvm",
+            "-c",
+            "src/polkavm_guest.c",
+            "-o",
+            bitcode_path,
+        ])
+        .output()
+        .expect("should be able to invoke C clang");
+
+    assert!(
+        output.status.success(),
+        "failed to compile the PolkaVM C API: {:?}",
+        output
+    );
+}
+
+fn main() {
+    let out_dir = env::var_os("OUT_DIR").expect("env should have $OUT_DIR");
+    let lib = "polkavm_guest.bc";
+    let bitcode_path = Path::new(&out_dir).join(lib);
+    compile(bitcode_path.to_str().expect("$OUT_DIR should be UTF-8"));
+
+    let bitcode = fs::read(bitcode_path).expect("bitcode should have been built");
+    let len = bitcode.len();
+    let src_path = Path::new(&out_dir).join("polkavm_guest.rs");
+    let src = format!("pub static BITCODE: &[u8; {len}] = include_bytes!(\"{lib}\");");
+    fs::write(src_path, src).expect("should be able to write in $OUT_DIR");
+
+    println!("cargo:rerun-if-changed=build.rs");
+    println!("cargo:rerun-if-changed=src/polkavm_guest.c");
+    println!("cargo:rerun-if-changed=src/polkavm_guest.h");
+}