[scudo] Fix inconsistent signed/unsigned comparison

[Chia-hungDuan]

Summary

Fix broken test on PPC

[chelfi]

Sorry for not catching this issue before, and thanks for fixing it!

compiler-rt/lib/scudo/standalone/tests/scudo_hooks_test.cpp

// Simple no-op, same size reallocation.
     LastAllocatedPtr = nullptr;
     LastRequestSize = 0;
     LastDeallocatedPtr = nullptr;
 
     void *NewPtr = Allocator.reallocate(Ptr, DefaultSize);
 
     EXPECT_EQ(Ptr, NewPtr);
     EXPECT_EQ(nullptr, LastAllocatedPtr);
-    EXPECT_EQ(0, LastRequestSize);
+    EXPECT_EQ(0U, LastRequestSize);
     EXPECT_EQ(nullptr, LastDeallocatedPtr);
   }
 
   // Reallocation in increasing size classes. This ensures that at
   // least one of the reallocations will be meaningful.
   {
     void *Ptr = Allocator.allocate(0, Origin);
 
for (scudo::uptr ClassId = 1U;
       void *NewPtr = Allocator.reallocate(Ptr, Size);
 
       if (NewPtr != Ptr) {
         EXPECT_EQ(NewPtr, LastAllocatedPtr);
         EXPECT_EQ(Size, LastRequestSize);
         EXPECT_EQ(Ptr, LastDeallocatedPtr);
       } else {
         EXPECT_EQ(nullptr, LastAllocatedPtr);
-        EXPECT_EQ(0, LastRequestSize);
+        EXPECT_EQ(0U, LastRequestSize);
         EXPECT_EQ(nullptr, LastDeallocatedPtr);
       }
 
       Ptr = NewPtr;
     }
   }
 }