Add new feature to allow building ckb-std using clang as C compiler

.github/workflows/build-with-clang.yml

@@ -0,0 +1,19 @@
+name: Build with clang
+
+on: [push, pull_request]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v3
+      with:
+        submodules: true
+    - name: Install llvm 16
+      run: wget https://apt.llvm.org/llvm.sh && chmod +x llvm.sh && sudo ./llvm.sh 16 && rm llvm.sh
+    - name: Install riscv64 target
+      run: rustup target add riscv64imac-unknown-none-elf
+    - name: Build
+      run: cargo build --verbose --target=riscv64imac-unknown-none-elf --features=build-with-clang

Cargo.toml

@@ -21,6 +21,7 @@ calc-hash = ["ckb-types/calc-hash"]
 allocator = ["buddy-alloc"]
 simulator = ["ckb-x64-simulator"]
 dlopen-c = []
+build-with-clang = []
 dummy-libc = []
 rustc-dep-of-std = [
     "alloc",

build.rs

@@ -7,7 +7,8 @@ fn main() {
     // ckb-std only supports riscv64 target arch
     // but we can still use cargo check under other archs
     if target_arch == "riscv64" && cfg!(feature = "dlopen-c") {
-        cc::Build::new()
+        let mut build = cc::Build::new();
+        build
             .file("dl-c-impl/lib.c")
             .static_flag(true)
             .flag("-O3")
@@ -24,11 +25,26 @@ fn main() {
             .flag("-Werror")
             .flag("-Wno-unused-parameter")
             .flag("-Wno-nonnull")
-            .define("__SHARED_LIBRARY__", None)
-            .flag("-Wno-nonnull-compare")
-            .flag("-nostartfiles")
-            .flag("-Wno-dangling-pointer")
-            .compile("dl-c-impl");
+            .define("__SHARED_LIBRARY__", None);
+
+        if cfg!(feature = "build-with-clang") {
+            let clang = match std::env::var_os("CLANG") {
+                Some(val) => val,
+                None => "clang-16".into(),
+            };
+
+            build
+                .compiler(clang)
+                .no_default_flags(true)
+                .flag("--target=riscv64")
+                .flag("-march=rv64imc_zba_zbb_zbc_zbs");
+        } else {
+            build
+                .flag("-nostartfiles")
+                .flag("-Wno-dangling-pointer")
+                .flag("-Wno-nonnull-compare");
+        }
+        build.compile("dl-c-impl");
     }
 
     if target_arch == "riscv64" && target_os == "ckb" && cfg!(feature = "dummy-libc") {