lang: Add pin and unpin

This patch adds pin/unpin lang items to the compiler but not fully tested
due to issues #4709 and #4678 so we tested
auto trait and negative impls behaviors.

gcc/rust/ChangeLog:

	* util/rust-lang-item.cc (Rust::LangItem::lang_items): Add pin
	and unpin lang items to the BiMap.
	* util/rust-lang-item.h (class LangItem): Add PIN and UNPIN to
	the Kind enum.

gcc/testsuite/ChangeLog:

	* rust/compile/lang-pin-unpin.rs: New test.

Signed-off-by: Enes Cevik <enes@nsvke.com>

Author: nsvke

gcc/rust/util/rust-lang-item.cc

@@ -144,6 +144,8 @@ const BiMap<std::string, LangItem::Kind> Rust::LangItem::lang_items = {{
   {"generator_state", Kind::GENERATOR_STATE},
 
   {"va_list", Kind::VA_LIST},
+  {"pin", Kind::PIN},
+  {"unpin", Kind::UNPIN},
 }};
 
 tl::optional<LangItem::Kind>

gcc/rust/util/rust-lang-item.h

@@ -180,6 +180,8 @@ class LangItem
     GENERATOR_STATE,
 
     VA_LIST,
+    PIN,
+    UNPIN,
   };
 
   static const BiMap<std::string, Kind> lang_items;

gcc/testsuite/rust/compile/lang-pin-unpin.rs

@@ -0,0 +1,38 @@
+#![feature(no_core, lang_items, optin_builtin_traits, negative_impls)]
+#![no_core]
+
+#[lang = "sized"]
+pub trait Sized {}
+
+#[lang = "unpin"]
+pub auto trait Unpin {}
+
+#[lang = "pin"]
+pub struct Pin<P> {
+    pointer: P,
+}
+
+impl<P> Pin<P> {
+    pub fn new(pointer: P) -> Pin<P>
+    where
+        P: Unpin,
+    {
+        Pin { pointer }
+    }
+}
+
+struct PhantomPinned;
+impl !Unpin for PhantomPinned {}
+
+struct PinnedStruct {
+    _marker: PhantomPinned, 
+}
+
+struct NormalStruct;
+
+fn main() {
+    let _ = Pin::new(NormalStruct); 
+
+    let pinned = PinnedStruct { _marker: PhantomPinned };
+    let _ = Pin::new(pinned); // { dg-error "bounds not satisfied for PinnedStruct .Unpin. is not satisfied .E0277." }
+}