[clang-tidy] Refactor: Move llvm clang-tidy checks to namespace clang::tidy::llvm

clang-tidy checks are organized into modules. This refactoring moves the llvm
module checks to clang::tidy::llvm

http://reviews.llvm.org/D7995

Patch by Richard Thomson!

llvm-svn: 230952
diff --git a/clang-tools-extra/clang-tidy/llvm/HeaderGuardCheck.h b/clang-tools-extra/clang-tidy/llvm/HeaderGuardCheck.h
index 82635b3..f5c509a 100644
--- a/clang-tools-extra/clang-tidy/llvm/HeaderGuardCheck.h
+++ b/clang-tools-extra/clang-tidy/llvm/HeaderGuardCheck.h
@@ -14,6 +14,7 @@
 
 namespace clang {
 namespace tidy {
+namespace llvm {
 
 /// Finds and fixes header guards that do not adhere to LLVM style.
 class LLVMHeaderGuardCheck : public HeaderGuardCheck {
@@ -25,6 +26,7 @@
   std::string getHeaderGuard(StringRef Filename, StringRef OldGuard) override;
 };
 
+} // namespace llvm
 } // namespace tidy
 } // namespace clang