Add rust wrappers over LLVM plugin API

This commit adds:
- the main crate implementing FFI over LLVM C++ API
- a minimal C++ static lib interfacing with the above crate
- a proc-macro crate providing a user-friendly syntax for using
the above crate to implement LLVM plugins

Author: jamesmth

.gitignore

@@ -1,10 +1,4 @@
-# Generated by Cargo
-# will have compiled files and executables
-/target/
-
-# Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
-# More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html
-Cargo.lock
-
-# These are backup files generated by rustfmt
 **/*.rs.bk
+**/target
+/.cache
+**/Cargo.lock

Cargo.toml

@@ -0,0 +1,6 @@
+[workspace]
+
+members = [
+    "llvm-plugin",
+    "llvm-plugin-macros",
+]

llvm-plugin-macros/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "llvm-plugin-macros"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+proc-macro2 = { version = "1", default-features = false }
+syn = { version = "1", features = ["full"] }
+quote = {version = "1", default-features = false }