Rewrite LLVM's archive writer in Rust

This allows it to be used by other codegen backends

compiler/rustc_codegen_gcc/Cargo.lock

@@ -11,12 +11,6 @@ dependencies = [
  "memchr",
 ]
 
-[[package]]
-name = "ar"
-version = "0.8.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "450575f58f7bee32816abbff470cbc47797397c2a81e0eaced4b98436daf52e1"
-
 [[package]]
 name = "bitflags"
 version = "1.3.2"
@@ -212,10 +206,8 @@ dependencies = [
 name = "rustc_codegen_gcc"
 version = "0.1.0"
 dependencies = [
- "ar",
  "gccjit",
  "lang_tester",
- "target-lexicon",
  "tempfile",
 ]
 
@@ -228,12 +220,6 @@ dependencies = [
  "winapi-util",
 ]
 
-[[package]]
-name = "target-lexicon"
-version = "0.10.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ab0e7238dcc7b40a7be719a25365910f6807bd864f4cce6b2e6b873658e2b19d"
-
 [[package]]
 name = "tempfile"
 version = "3.2.0"