Meta: Remove rlibc now that upstream issue is fixed

This issue made it impossible to use -Zbuild-std without implementing
the memory related symbols required by the core lib such as memcpy,
memset, etc yourself.

rust-lang/wg-cargo-std-aware#53

After this PR you can now tell cargo that your platform supports these
mem features and just use the built in implementations in rustc.

.cargo/config → .cargo/config.toml

@@ -6,3 +6,4 @@ runner = "bootimage runner --quiet"
 
 [unstable]
 build-std = ["core", "compiler_builtins", "alloc"]
+build-std-features = ["compiler-builtins-mem"]

Cargo.toml

@@ -8,7 +8,6 @@ edition = "2018"
 bootloader = { version = "0.9", features = ["map_physical_memory"] }
 lazy_static = { version = "1.4", features = ["spin_no_std"] }
 spin = "0.5"
-rlibc = "1.0"
 
 [package.metadata.bootimage]
 run-args = ["-serial", "stdio"]

src/lib.rs

@@ -9,11 +9,6 @@
 #![allow(clippy::missing_safety_doc)] // library lints
 #![allow(clippy::new_without_default)]
 
-// When using cargo's -Zbuild-std some symbols like memcpy, memset etc are not
-// included, so we need to depend on this crate until this issue is fixed:
-// https://github.com/rust-lang/wg-cargo-std-aware/issues/53
-extern crate rlibc;
-
 #[macro_use]
 pub mod dbg_print;
 pub mod interrupts;