Add and use more static symbols.

Note that the output of `unpretty-debug.stdout` has changed. In that
test the hash values are normalized from a symbol numbers to small
numbers like "0#0" and "0#1". The increase in the number of static
symbols must have caused the original numbers to contain more digits,
resulting in different pretty-printing prior to normalization.

src/test/ui/hygiene/unpretty-debug.stdout

@@ -10,7 +10,10 @@
 
 macro_rules! foo /* 0#0 */ { ($ x : ident) => { y + $ x } }
 
-fn bar /* 0#0 */() { let x /* 0#0 */ = 1; y /* 0#1 */ + x /* 0#0 */ }
+fn bar /* 0#0 */() {
+    let x /* 0#0 */ = 1;
+    y /* 0#1 */ + x /* 0#0 */
+}
 
 fn y /* 0#0 */() { }