fix: overflow (oceanbase#309)

### What problems were solved in this pull request?

Problem: `compare_int` uses subtraction to determine the size of two
integers, which may cause integer overflow and return incorrect results.

### How to reproduce

When v1 is -2147483648 and v2 is 1, return 2147483647. Returned
incorrect result due to integer overflow

### What is changed and how it works?

Use comparison operators instead of subtraction.

deps/common/lang/comparator.cpp

@@ -23,7 +23,13 @@ int compare_int(void *arg1, void *arg2)
 {
   int v1 = *(int *)arg1;
   int v2 = *(int *)arg2;
-  return v1 - v2;
+  if (v1 > v2) {
+    return 1;
+  } else if (v1 < v2) {
+    return -1;
+  } else {
+    return 0;
+  }
 }
 
 int compare_float(void *arg1, void *arg2)