Rollup merge of rust-lang#58865 - dlrobertson:fix-varargs, r=alexreg

Fix C-variadic function printing

There is no longer a need to append the string `", ..."` to a functions
args as `...` is parsed as an argument and will appear in the functions
arguments.

r? @alexreg
cc @alexcrichton
Fixes: rust-lang#58853

Author: Mark-Simulacrum

src/libsyntax/print/pprust.rs

@@ -2814,9 +2814,6 @@ impl<'a> State<'a> {
         -> io::Result<()> {
         self.popen()?;
         self.commasep(Inconsistent, &decl.inputs, |s, arg| s.print_arg(arg, false))?;
-        if decl.c_variadic {
-            self.s.word(", ...")?;
-        }
         self.pclose()?;
 
         self.print_fn_output(decl)

src/test/pretty/fn-variadic.rs

@@ -0,0 +1,15 @@
+// Check that `fn foo(x: i32, ...)` does not print as `fn foo(x: i32, ..., ...)`.
+// See issue #58853.
+
+// pp-exact
+#![feature(c_variadic)]
+
+extern "C" {
+    pub fn foo(x: i32, ...);
+}
+
+pub unsafe extern "C" fn bar(_: i32, mut ap: ...) -> usize {
+    ap.arg::<usize>()
+}
+
+fn main() {}