Use raw syscall numbers

Cargo.toml

@@ -46,7 +46,6 @@ shell-escape = "0.1.4"
 rustc-workspace-hack = "1.0.0"
 hex = "0.3.2"
 rand = "0.6.5"
-libc = "0.2.51"
 
 [build-dependencies]
 vergen = "3"

src/fn_call.rs

@@ -217,7 +217,8 @@ pub trait EvalContextExt<'a, 'mir, 'tcx: 'a + 'mir>: crate::MiriEvalContextExt<'
                 // `libc::syscall(NR_GETRANDOM, buf.as_mut_ptr(), buf.len(), GRND_NONBLOCK)`
                 // is called if a `HashMap` is created the regular way.
                 match this.read_scalar(args[0])?.to_usize(this)? as i64 {
-                    libc::SYS_getrandom => {
+                    // SYS_getrandom on x86_64 and x86 respectively
+                    318 | 355 => {
                         match this.machine.rng.as_ref() {
                             Some(rng) => {
                                 let ptr = this.read_scalar(args[1])?.to_ptr()?;