[PATCH] [clang-tidy] Add a generic header guard checker + LLVM implementation.

[Alexander Kornienko]

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Comment at: clang-tidy/utils/HeaderGuard.cpp:126
@@ +125,3 @@
+    // Emit warnings for headers that are missing guards.
+    checkGuardlessHeaders();
+  }
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This class is stateful. AFAIU, it's reused when a tool is run with several translation units (clang-tidy x.cpp y.cpp z.cpp), so it should clean its state here.

http://reviews.llvm.org/D4867