feat: add libc feature for linking to the C library

Signed-off-by: Martin Kröning <[email protected]>

hermit/Cargo.toml

@@ -37,6 +37,7 @@ idle-poll = []
 # Build the kernel with function instrument code for mcount-based tracing
 instrument = []
 
+libc = []
 mmap = []
 pci = []
 pci-ids = ["pci"]
@@ -57,6 +58,7 @@ vga = []
 vsock = []
 
 [build-dependencies]
+cc = "1"
 flate2 = "1"
 ureq = "2.4"
 tar = "0.4"

hermit/build.rs

@@ -18,6 +18,18 @@ fn main() {
 	let kernel_src = KernelSrc::local().unwrap_or_else(KernelSrc::download);
 
 	kernel_src.build();
+
+	if has_feature("libc") {
+		let libc = cc::Build::new()
+			.get_compiler()
+			.to_command()
+			.arg("-print-file-name=libc.a")
+			.output()
+			.unwrap()
+			.stdout;
+		let libc = str::from_utf8(&libc).unwrap().trim_ascii_end();
+		println!("cargo:rustc-link-lib=static:+verbatim={libc}");
+	}
 }
 
 struct KernelSrc {