Add a UI test related to feature-gated primitives

Add a test that `f16` and `f128` are usable with the feature gate
enabled, as well as a test that user types with the same name as
primitives are not improperly gated.

tests/ui/resolve/conflicting-primitive-names.rs

@@ -0,0 +1,30 @@
+//@ check-pass
+#![allow(non_camel_case_types)]
+#![allow(unused)]
+
+// Ensure that primitives do not interfere with user types of similar names
+
+macro_rules! make_ty_mod {
+    ($modname:ident, $ty:tt) => {
+        mod $modname {
+            struct $ty {
+                a: i32,
+            }
+
+            fn assignment() {
+                let $ty = ();
+            }
+
+            fn access(a: $ty) -> i32 {
+                a.a
+            }
+        }
+    };
+}
+
+make_ty_mod!(check_f16, f16);
+make_ty_mod!(check_f32, f32);
+make_ty_mod!(check_f64, f64);
+make_ty_mod!(check_f128, f128);
+
+fn main() {}

tests/ui/resolve/primitive-f128.rs

@@ -0,0 +1,18 @@
+//@ check-pass
+#![feature(f128)]
+
+// Same as the feature gate test but ensure we can use the types
+
+const A: f128 = 10.0;
+
+pub fn main() {
+    let a: f128 = 100.0;
+    let b = 0.0f128;
+    foo(1.23);
+}
+
+fn foo(a: f128) {}
+
+struct Bar {
+    a: f128,
+}

tests/ui/resolve/primitive-f16.rs

@@ -0,0 +1,18 @@
+//@ check-pass
+#![feature(f16)]
+
+// Same as the feature gate test but ensure we can use the types
+
+const A: f16 = 10.0;
+
+pub fn main() {
+    let a: f16 = 100.0;
+    let b = 0.0f16;
+    foo(1.23);
+}
+
+fn foo(a: f16) {}
+
+struct Bar {
+    a: f16,
+}