Add check for other variadic functions

src/shims/unix/android/thread.rs

@@ -19,6 +19,7 @@ pub fn prctl<'tcx>(
     // We do not use `check_shim` here because `prctl` is variadic. The argument
     // count is checked bellow.
     ecx.check_abi_and_shim_symbol_clash(abi, Conv::C, link_name)?;
+    ecx.check_fixed_args_count("prctl", abi, 1)?;
 
     // FIXME: Use constants once https://github.com/rust-lang/libc/pull/3941 backported to the 0.2 branch.
     let pr_set_name = 15;

src/shims/unix/foreign_items.rs

@@ -208,6 +208,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 // `fcntl` is variadic. The argument count is checked based on the first argument
                 // in `this.fcntl()`, so we do not use `check_shim` here.
                 this.check_abi_and_shim_symbol_clash(abi, Conv::C , link_name)?;
+                this.check_fixed_args_count("fcntl", abi, 2)?;
                 let result = this.fcntl(args)?;
                 this.write_scalar(result, dest)?;
             }

src/shims/unix/linux_like/syscall.rs

@@ -17,6 +17,7 @@ pub fn syscall<'tcx>(
     // We do not use `check_shim` here because `syscall` is variadic. The argument
     // count is checked bellow.
     ecx.check_abi_and_shim_symbol_clash(abi, Conv::C, link_name)?;
+    ecx.check_fixed_args_count("syscall", abi, 1)?;
     // The syscall variadic function is legal to call with more arguments than needed,
     // extra arguments are simply ignored. The important check is that when we use an
     // argument, we have to also check all arguments *before* it to ensure that they