Clang: Sort file path ids

We will move that code to an other place where we will implement the tests
for the sorting.

Change-Id: Ia6e868466e2c43acdc0f5a8ed73b32cfc24613c1
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/libs/clangsupport/filepathcachinginterface.h

@@ -56,6 +56,8 @@ public:
                       std::back_inserter(filePathIds),
                       [&] (const auto &filePath) { return this->filePathId(filePath); });
 
+       std::sort(filePathIds.begin(), filePathIds.end());
+
        return filePathIds;
     }