Fix line break after ":" in unpretty attribute print

Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>

compiler/rustc_macros/src/print_attribute.rs

@@ -21,7 +21,8 @@ fn print_fields(name: &Ident, fields: &Fields) -> (TokenStream, TokenStream, Tok
                             __p.word_space(",");
                         }
                         __p.word(#string_name);
-                        __p.word_space(":");
+                        __p.word(":");
+                        __p.nbsp();
                         __printed_anything = true;
                     }
                     #name.print_attribute(__p);

tests/ui/unpretty/deprecated-attr.stdout

@@ -9,12 +9,12 @@ extern crate std;
 #[attr = Deprecation {deprecation: Deprecation {since: Unspecified}}]
 struct PlainDeprecated;
 
-#[attr = Deprecation {deprecation: Deprecation {since: Unspecified, note:
-"here's why this is deprecated"}}]
+#[attr = Deprecation {deprecation: Deprecation {since: Unspecified,
+note: "here's why this is deprecated"}}]
 struct DirectNote;
 
-#[attr = Deprecation {deprecation: Deprecation {since: Unspecified, note:
-"here's why this is deprecated"}}]
+#[attr = Deprecation {deprecation: Deprecation {since: Unspecified,
+note: "here's why this is deprecated"}}]
 struct ExplicitNote;
 
 #[attr = Deprecation {deprecation: Deprecation {since: NonStandard("1.2.3"),
@@ -28,8 +28,6 @@ struct FlippedOrder;
 fn f() {
 
     // Attribute is ignored here (with a warning), but still preserved in HIR
-    #[attr = Deprecation {deprecation:
-    Deprecation {since:
-    Unspecified}}]
+    #[attr = Deprecation {deprecation: Deprecation {since: Unspecified}}]
     0
 }

tests/ui/unpretty/exhaustive.hir.stdout

@@ -64,8 +64,7 @@ mod attributes {
     #[doc = "outer doc attribute"]
     #[doc = "macro"]
     #[allow()]
-    #[attr = Repr {reprs:
-    [ReprC]}]
+    #[attr = Repr {reprs: [ReprC]}]
     struct Struct;
 }