Subzero: Use a proper RegNumT type instead of int32_t/SizeT.

src/IceRegistersX8632.h

Index: src/IceRegistersX8632.h
diff --git a/src/IceRegistersX8632.h b/src/IceRegistersX8632.h
index 5d71aa70a7612564922d319ae6eb4f906645b23c..bb614e0c905bff72733a57d42778aed2272e82ff 100644
--- a/src/IceRegistersX8632.h
+++ b/src/IceRegistersX8632.h
@@ -80,10 +80,10 @@ public:
         Encoded_Not_X87STReg = -1
   };
 
-  static inline X87STRegister getEncodedSTReg(int32_t RegNum) {
-    assert(Encoded_X87ST_First <= RegNum);
-    assert(RegNum <= Encoded_X87ST_Last);
-    return X87STRegister(RegNum);
+  static inline X87STRegister getEncodedSTReg(uint32_t X87RegNum) {
+    assert(int(Encoded_X87ST_First) <= int(X87RegNum));
+    assert(X87RegNum <= Encoded_X87ST_Last);
+    return X87STRegister(X87RegNum);
   }
 };