Fix g++ -pedantic warnings.

1. Comma-terminated enumerator lists.
2. Empty macro arguments.
3. Variable-length arrays.

The first issue is definitely hitting the Mac bots.  The other two issues will quite possibly following that.

BUG= none
R=jfb@chromium.org

Review URL: https://codereview.chromium.org/296823013
diff --git a/src/IceInst.h b/src/IceInst.h
index 3067c26..fd0eeea 100644
--- a/src/IceInst.h
+++ b/src/IceInst.h
@@ -161,6 +161,7 @@
 #define X(tag, str, commutative) tag,
     ICEINSTARITHMETIC_TABLE
 #undef X
+        _num
   };
 
   static InstArithmetic *create(Cfg *Func, OpKind Op, Variable *Dest,
@@ -287,6 +288,7 @@
 #define X(tag, str) tag,
     ICEINSTCAST_TABLE
 #undef X
+        _num
   };
 
   static InstCast *create(Cfg *Func, OpKind CastKind, Variable *Dest,
@@ -314,6 +316,7 @@
 #define X(tag, str) tag,
     ICEINSTFCMP_TABLE
 #undef X
+        _num
   };
 
   static InstFcmp *create(Cfg *Func, FCond Condition, Variable *Dest,
@@ -342,6 +345,7 @@
 #define X(tag, str) tag,
     ICEINSTICMP_TABLE
 #undef X
+        _num
   };
 
   static InstIcmp *create(Cfg *Func, ICond Condition, Variable *Dest,