hermit-builtins: Build mem via build-std-features

See #627 (comment)

Author: mkroening

hermit-builtins/Cargo.lock

@@ -5,6 +5,3 @@ edition = "2021"
 
 [lib]
 crate-type = ["staticlib"]
-
-[dependencies]
-mem-builtins = { package = "compiler_builtins", version = "0.1", features = ["mem"] }

hermit-builtins/Cargo.toml

@@ -1,7 +1,5 @@
 #![no_std]
 
-use mem_builtins as _;
-
 #[panic_handler]
 fn panic(_info: &core::panic::PanicInfo) -> ! {
 	loop {}

hermit-builtins/src/lib.rs

@@ -32,8 +32,16 @@ impl Arch {
 
 	pub fn builtins_cargo_args(&self) -> &'static [&'static str] {
 		match self {
-			Arch::X86_64 => &["--target=x86_64-unknown-hermit", "-Zbuild-std=core"],
-			Arch::AArch64 => &["--target=aarch64-unknown-hermit", "-Zbuild-std=core"],
+			Arch::X86_64 => &[
+				"--target=x86_64-unknown-hermit",
+				"-Zbuild-std=core",
+				"-Zbuild-std-features=compiler-builtins-mem",
+			],
+			Arch::AArch64 => &[
+				"--target=aarch64-unknown-hermit",
+				"-Zbuild-std=core",
+				"-Zbuild-std-features=compiler-builtins-mem",
+			],
 		}
 	}