cmDependsC: Read cache file modification time only once

Using cmFileTime to store and compare file times in cmDependsC allows us to
read the cache file modification time only once instead of over and over again
for each comparison.

Source/cmDependsC.cxx

@@ -6,6 +6,7 @@
 #include <utility>
 
 #include "cmAlgorithms.h"
+#include "cmFileTime.h"
 #include "cmLocalGenerator.h"
 #include "cmMakefile.h"
 #include "cmSystemTools.h"
@@ -247,6 +248,8 @@ void cmDependsC::ReadCacheFile()
   cmIncludeLines* cacheEntry = nullptr;
   bool haveFileName = false;
 
+  cmFileTime cacheFileTime;
+  bool const cacheFileTimeGood = cacheFileTime.Load(this->CacheFileName);
   while (cmSystemTools::GetLineFromStream(fin, line)) {
     if (line.empty()) {
       cacheEntry = nullptr;
@@ -256,11 +259,12 @@ void cmDependsC::ReadCacheFile()
     // the first line after an empty line is the name of the parsed file
     if (!haveFileName) {
       haveFileName = true;
-      int newer = 0;
-      bool res =
-        cmSystemTools::FileTimeCompare(this->CacheFileName, line, &newer);
 
-      if (res && newer == 1) // cache is newer than the parsed file
+      cmFileTime fileTime;
+      bool const res = cacheFileTimeGood && fileTime.Load(line);
+      bool const newer = res && cacheFileTime.Newer(fileTime);
+
+      if (res && newer) // cache is newer than the parsed file
       {
         cacheEntry = new cmIncludeLines;
         this->FileCache[line] = cacheEntry;