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

src/IceRegistersMIPS32.h

Index: src/IceRegistersMIPS32.h
diff --git a/src/IceRegistersMIPS32.h b/src/IceRegistersMIPS32.h
index 89c4d8925da229eb9bfb6bb07674f9fe53c38068..a7072841ed14e9c92964c8cb36cc108b260219f5 100644
--- a/src/IceRegistersMIPS32.h
+++ b/src/IceRegistersMIPS32.h
@@ -53,12 +53,13 @@ enum GPRRegister {
 // TODO(jvoung): Floating point and vector registers...
 // Need to model overlap and difference in encoding too.
 
-static inline GPRRegister getEncodedGPR(int32_t RegNum) {
-  assert(Reg_GPR_First <= RegNum && RegNum <= Reg_GPR_Last);
+static inline GPRRegister getEncodedGPR(RegNumT RegNum) {
+  assert(int(Reg_GPR_First) <= int(RegNum));
+  assert(unsigned(RegNum) <= Reg_GPR_Last);
   return GPRRegister(RegNum - Reg_GPR_First);
 }
 
-const char *getRegName(int32_t RegNum);
+const char *getRegName(RegNumT RegNum);
 
 } // end of namespace RegMIPS32