Fixes test failure on arm.

https://github.com/unicode-org/icu/pull/1925
https://unicode-org.atlassian.net/browse/ICU-21793

From: =?UTF-8?q?J=C3=A9r=C3=A9my=20Lal?= <kapouer@melix.org>
Date: Wed, 3 Nov 2021 02:31:18 +0100
Subject: [PATCH] ICU-21793 Fix ucptrietest golden diff

--- a/source/tools/toolutil/toolutil.cpp
+++ b/source/tools/toolutil/toolutil.cpp
@@ -228,18 +228,19 @@ uprv_compareGoldenFiles(
     std::ifstream ifs(goldenFilePath, std::ifstream::in);
     int32_t pos = 0;
     char c;
-    while ((c = ifs.get()) != std::char_traits<char>::eof() && pos < bufferLen) {
+    while (ifs.get(c) && pos < bufferLen) {
         if (c != buffer[pos]) {
             // Files differ at this position
-            return pos;
+            break;
         }
         pos++;
     }
-    if (pos < bufferLen || c != std::char_traits<char>::eof()) {
-        // Files are different lengths
-        return pos;
+    if (pos == bufferLen && ifs.eof()) {
+        // Files are same lengths
+        pos = -1;
     }
-    return -1;
+    ifs.close();
+    return pos;
 }

 /*U_CAPI UDate U_EXPORT2

