revive llvm builder utility (#154)

Pre-eliminary support for LLVM releases and resolc binary releases by streamlining the build process for all supported hosts platforms.

- Introduce the revive-llvm-builder crate with the revive-llvm builder utilty.
- Do not rely on the LLVM dependency in $PATH to decouple the system LLVM installation from the LLVM host dependency.
- Fix the emscripten build by decoupling the host and native LLVM dependencies. Thus allowing a single LLVM emscripten release that can be used on any host platform.
- An example Dockerfile building an alpine container with a fully statically linked resolc ELF binary.
- Remove the Debian builder utilities and workflow.

crates/build-utils/src/lib.rs

@@ -0,0 +1,48 @@
+//! The compiler build utilities library.
+
+/// The revive LLVM host dependency directory prefix environment variable.
+pub const REVIVE_LLVM_HOST_PREFIX: &str = "LLVM_SYS_181_PREFIX";
+
+/// The revive LLVM target dependency directory prefix environment variable.
+pub const REVIVE_LLVM_TARGET_PREFIX: &str = "REVIVE_LLVM_TARGET_PREFIX";
+
+/// Constructs a path to the LLVM tool `name`.
+///
+/// Respects the [`REVIVE_LLVM_HOST_PREFIX`] environment variable.
+pub fn llvm_host_tool(name: &str) -> std::path::PathBuf {
+    std::env::var_os(REVIVE_LLVM_HOST_PREFIX)
+        .map(Into::<std::path::PathBuf>::into)
+        .unwrap_or_else(|| {
+            panic!(
+                "install LLVM using the revive-llvm builder and export {REVIVE_LLVM_HOST_PREFIX}",
+            )
+        })
+        .join("bin")
+        .join(name)
+}
+
+/// Returns the LLVM lib dir.
+///
+/// Respects the [`REVIVE_LLVM_HOST_PREFIX`] environment variable.
+pub fn llvm_lib_dir() -> std::path::PathBuf {
+    std::path::PathBuf::from(llvm_config("--libdir").trim())
+}
+
+/// Returns the LLVM CXX compiler flags.
+///
+/// Respects the [`REVIVE_LLVM_HOST_PREFIX`] environment variable.
+pub fn llvm_cxx_flags() -> String {
+    llvm_config("--cxxflags")
+}
+
+/// Execute the `llvm-config` utility respecting the [`REVIVE_LLVM_HOST_PREFIX`] environment variable.
+fn llvm_config(arg: &str) -> String {
+    let llvm_config = llvm_host_tool("llvm-config");
+    let output = std::process::Command::new(&llvm_config)
+        .arg(arg)
+        .output()
+        .unwrap_or_else(|error| panic!("`{} {arg}` failed: {error}", llvm_config.display()));
+
+    String::from_utf8(output.stdout)
+        .unwrap_or_else(|_| panic!("output of `{} {arg}` should be utf8", llvm_config.display()))
+}