bootstrap: Add a bunch of Cargo.toml files

These describe the structure of all our crate dependencies.

src/liballoc_system/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+authors = ["The Rust Project Developers"]
+name = "alloc_system"
+version = "0.0.0"
+
+[lib]
+name = "alloc_system"
+path = "lib.rs"
+test = false
+
+[dependencies]
+core = { path = "../libcore" }
+libc = { path = "../rustc/libc_shim" }