Use compiler_builtins mem feature instead of rlibc

Also: Update x86_64 to 0.12.2 to fix build on latest nightly.

Author: phil-opp

Cargo.lock

@@ -35,7 +35,6 @@ xmas-elf = { version = "0.6.2", optional = true }
 x86_64 = { git = "https://github.com/rust-osdev/x86_64.git", branch = "access-level-4-table", optional = true }
 usize_conversions = { version = "0.2.0", optional = true }
 bit_field = { version = "0.10.0", optional = true }
-rlibc = { version = "1.0.0", optional = true }
 log = { version = "0.4.8", optional = true }
 uefi = { version = "0.6.0", optional = true }
 argh = { version = "0.1.3", optional = true }
@@ -62,8 +61,8 @@ toml = { version = "0.5.1", optional = true }
 default = []
 builder = ["argh", "thiserror", "displaydoc", "anyhow", "llvm-tools", "json"]
 runner = ["anyhow"]
-bios_bin = ["binary", "rlibc", "vga_320x200", "rsdp"]
-uefi_bin = ["binary", "rlibc", "uefi", "font8x8"]
+bios_bin = ["binary", "vga_320x200", "rsdp"]
+uefi_bin = ["binary", "uefi", "font8x8"]
 binary = ["llvm-tools-build", "x86_64", "toml", "xmas-elf", "usize_conversions", "log", "conquer-once",  "spinning_top"]
 vga_320x200 = ["font8x8"]
 recursive_page_table = []

Cargo.toml

@@ -9,8 +9,6 @@
 #[cfg(not(target_os = "none"))]
 compile_error!("The bootloader crate must be compiled for the `x86_64-bootloader.json` target");
 
-extern crate rlibc;
-
 use bootloader::{binary::SystemInfo, boot_info::FrameBufferInfo};
 use core::panic::PanicInfo;
 use core::slice;

src/bin/bios.rs

@@ -81,6 +81,7 @@ fn main() -> anyhow::Result<()> {
         cmd.arg("--features")
             .arg(args.features.join(" ") + " uefi_bin");
         cmd.arg("-Zbuild-std=core");
+        cmd.arg("-Zbuild-std-features=compiler-builtins-mem");
         if let Some(target_dir) = &args.target_dir {
             cmd.arg("--target-dir").arg(target_dir);
         }
@@ -101,6 +102,7 @@ fn main() -> anyhow::Result<()> {
         cmd.arg("--features")
             .arg(args.features.join(" ") + " bios_bin");
         cmd.arg("-Zbuild-std=core");
+        cmd.arg("-Zbuild-std-features=compiler-builtins-mem");
         if let Some(target_dir) = &args.target_dir {
             cmd.arg("--target-dir").arg(target_dir);
         }

src/bin/builder.rs

@@ -15,8 +15,6 @@ static KERNEL: PageAligned<[u8; KERNEL_SIZE]> = PageAligned(KERNEL_BYTES);
 #[repr(align(4096))]
 struct PageAligned<T>(T);
 
-extern crate rlibc;
-
 use bootloader::{
     binary::{legacy_memory_region::LegacyFrameAllocator, SystemInfo},
     boot_info::FrameBufferInfo,