CMakeProjectManager: Fix issues with precompiled headers

Clang code model can break if CMake project uses precompiled headers.

QtCreator will make a copy of the precompiled header, this way it
will not conflict with the build system one.

Ammends 888ea6bbbb

Fixes: QTCREATORBUG-24945
Fixes: QTCREATORBUG-25213
Change-Id: I149fc416cd047683d095758a024de47c7baf681c
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/libs/utils/fileutils.cpp

@@ -219,6 +219,29 @@ bool FileUtils::copyRecursively(const FilePath &srcFilePath, const FilePath &tgt
         });
 }
 
+/*!
+  Copies a file specified by \a srcFilePath to \a tgtFilePath only if \a srcFilePath is different
+  (file size and last modification time).
+
+  Returns whether the operation succeeded.
+*/
+
+bool FileUtils::copyIfDifferent(const FilePath &srcFilePath, const FilePath &tgtFilePath)
+{
+    if (QFile::exists(tgtFilePath.toString())) {
+        const QFileInfo srcFileInfo = srcFilePath.toFileInfo();
+        const QFileInfo tgtFileInfo = tgtFilePath.toFileInfo();
+        if (srcFileInfo.lastModified() == tgtFileInfo.lastModified() &&
+            srcFileInfo.size() == tgtFileInfo.size()) {
+            return true;
+        } else {
+            QFile::remove(tgtFilePath.toString());
+        }
+    }
+
+    return QFile::copy(srcFilePath.toString(), tgtFilePath.toString());
+}
+
 /*!
   If this is a directory, the function will recursively check all files and return
   true if one of them is newer than \a timeStamp. If this is a single file, true will