Rename cmFileTimeComparison to cmFileTimeCache

The name `cmFileTimeCache` reflects the functionality of the class more
appropriately.

Source/cmFileTimeCache.h

@@ -0,0 +1,52 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+#ifndef cmFileTimeCache_h
+#define cmFileTimeCache_h
+
+#include "cmConfigure.h" // IWYU pragma: keep
+
+#include "cmFileTime.h"
+#include <string>
+#include <unordered_map>
+
+/** \class cmFileTimeCache
+ * \brief Caches file modification times in an internal map for fast lookups.
+ */
+class cmFileTimeCache
+{
+public:
+  cmFileTimeCache();
+  ~cmFileTimeCache();
+
+  cmFileTimeCache(const cmFileTimeCache&) = delete;
+  cmFileTimeCache& operator=(const cmFileTimeCache&) = delete;
+
+  /**
+   * @brief Loads the file time from the cache or the file system.
+   * @return true on success
+   */
+  bool Load(std::string const& fileName, cmFileTime& fileTime);
+
+  /**
+   * @brief Compare file modification times.
+   * @return true for successful comparison and false for error.
+   *
+   * When true is returned, result has -1, 0, +1 for
+   * f1 older, same, or newer than f2.
+   */
+  bool FileTimeCompare(std::string const& f1, std::string const& f2,
+                       int* result);
+
+  /**
+   * @brief Compare file modification times.
+   * @return true unless both files exist and have modification times less
+   *         than 1 second apart.
+   */
+  bool FileTimesDiffer(std::string const& f1, std::string const& f2);
+
+private:
+  typedef std::unordered_map<std::string, cmFileTime> FileTimeMap;
+  FileTimeMap FileTimes;
+};
+
+#endif