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

[Manuel Klimek]

I still doubt we have enough tests. Otherwise LG.

================
Comment at: clang-tidy/utils/HeaderGuard.cpp:173
@@ +172,3 @@
+  /// \brief Looks for files that were visited but didn't have a header guard.
+  /// emits a warning with fixits suggesting adding one.
+  void checkGuardlessHeaders() {
----------------
s/emits/Emits/

================
Comment at: clang-tidy/utils/HeaderGuard.h:30-32
@@ +29,5 @@
+  virtual bool shouldFixHeaderGuard(StringRef Filename);
+  /// \brief Returns true if the checker should add a header guard to the file
+  /// if
+  /// it has none.
+  virtual bool shouldSuggestToAddHeaderGuard(StringRef Filename);
----------------
:gq

http://reviews.llvm.org/D4867