Fix cmpRunesIgnoreCase on system where sizeof(int) < 4. Fixes #23125. (#23138)

Fixes an issue where importing the `strutils` module, or any other
importing the `strutils` module, ends up with a compile time error on
platforms where ints are less then 32-bit wide.

The fix follows the suggestions made in #23125.

(cherry picked from commit 15c7b76c66)

lib/pure/unicode.nim

@@ -846,7 +846,12 @@ proc cmpRunesIgnoreCase*(a, b: openArray[char]): int {.rtl, extern: "nuc$1".} =
     # slow path:
     fastRuneAt(a, i, ar)
     fastRuneAt(b, j, br)
-    result = RuneImpl(toLower(ar)) - RuneImpl(toLower(br))
+    when sizeof(int) < 4:
+      const lo = low(int).int32
+      const hi = high(int).int32
+      result = clamp(RuneImpl(toLower(ar)) - RuneImpl(toLower(br)), lo, hi).int
+    else:
+      result = RuneImpl(toLower(ar)) - RuneImpl(toLower(br))
     if result != 0: return
   result = a.len - b.len