implement anon enums

Not sure if we want to keep this factoring, it just reuses the
old infrastructure for now. Passes the anon enum tests.

src/core/Enumeration.pm

@@ -46,3 +46,20 @@ my role NumericEnumeration {
         self.key
     }
 }
+
+sub ANON_ENUM(*@args) {
+    my Mu $prev = -1;
+    my %res;
+    for @args {
+        if .^isa(Enum) {
+            %res{.key} = .value;
+        }
+        else {
+            %res{$_} = $prev.=succ;
+        }
+    }
+    my $r := nqp::create(EnumMap);
+    nqp::bindattr($r, EnumMap, '$!storage',
+        nqp::getattr(%res, EnumMap, '$!storage'));
+    $r;
+}

src/core/stubs.pm

@@ -12,6 +12,7 @@ my class Seq is List does Positional { }
 my class Exception { ... }
 my class X::AdHoc  { ... }
 my class FatRat    { ... }
+my class Enum      { ... }
 
 sub DYNAMIC(\$name) is rw { 
     my Mu $x := pir::find_dynamic_lex__Ps(nqp::unbox_s($name));

t/spectest.data

@@ -424,7 +424,7 @@ S12-construction/BUILD.t
 S12-construction/construction.t
 S12-construction/named-params-in-BUILD.t
 S12-construction/new.t
-# S12-enums/anonymous.t # err: Undefined routine '&ANON_ENUM' called
+S12-enums/anonymous.t
 # S12-enums/as-role.t # err: Cannot yet turn an enum into a role
 S12-enums/basic.t
 S12-enums/misc.t