ir: Deal with _Atomic correctly.

Cargo.toml

@@ -50,7 +50,7 @@ bitflags = "1.0.3"
 cexpr = "0.6"
 # This kinda sucks: https://github.com/rust-lang/cargo/issues/1982
 clap = { version = "3", optional = true }
-clang-sys = { version = "1", features = ["clang_6_0"] }
+clang-sys = { version = "1", features = ["clang_11_0"] }
 lazycell = "1"
 lazy_static = "1"
 peeking_take_while = "0.1.2"

src/clang.rs

@@ -1068,6 +1068,15 @@ impl Type {
         }
     }
 
+    /// If this is an atomic type, returns the underlying value type, otherwise
+    /// an invalid type.
+    #[inline]
+    pub fn atomic_value_type(&self) -> Self {
+        Self {
+            x: unsafe { clang_Type_getValueType(self.x) },
+        }
+    }
+
     /// What is the size of this type? Paper over invalid types by returning `0`
     /// for them.
     pub fn size(&self, ctx: &BindgenContext) -> usize {

src/ir/context.rs

@@ -1970,6 +1970,10 @@ If you encounter an error missing from this list, please file an issue or a PR!"
             CXType_Double => TypeKind::Float(FloatKind::Double),
             CXType_LongDouble => TypeKind::Float(FloatKind::LongDouble),
             CXType_Float128 => TypeKind::Float(FloatKind::Float128),
+            CXType_Atomic => {
+                // TODO(#2151): Preserve atomicity in a useful way somehow.
+                return self.build_builtin_ty(&ty.atomic_value_type());
+            }
             CXType_Complex => {
                 let float_type =
                     ty.elem_type().expect("Not able to resolve complex type?");

tests/expectations/tests/atomic-constant.rs

@@ -0,0 +1,10 @@
+#![allow(
+    dead_code,
+    non_snake_case,
+    non_camel_case_types,
+    non_upper_case_globals
+)]
+
+extern "C" {
+    pub static mut interrupted: ::std::os::raw::c_uint;
+}

tests/headers/atomic-constant.h

@@ -0,0 +1 @@
+extern _Atomic unsigned interrupted;