[clang-tidy] Add check llvmlibc-implementation-in-namespace.

Summary:
This check makes sure all llvm-libc implementations falls within the `__llvm_libc` namespace.

Reviewers: alexfh, aaron.ballman, hokein, njames93

Reviewed By: aaron.ballman

Subscribers: Eugene.Zelenko, libc-commits, mgorny, xazax.hun, MaskRay, cfe-commits, sivachandra

Tags: #clang-tools-extra, #clang

Differential Revision: https://reviews.llvm.org/D76818
diff --git a/clang-tools-extra/clang-tidy/llvmlibc/LLVMLibcTidyModule.cpp b/clang-tools-extra/clang-tidy/llvmlibc/LLVMLibcTidyModule.cpp
index 9874cae..8c5a7ac 100644
--- a/clang-tools-extra/clang-tidy/llvmlibc/LLVMLibcTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/llvmlibc/LLVMLibcTidyModule.cpp
@@ -9,6 +9,7 @@
 #include "../ClangTidy.h"
 #include "../ClangTidyModule.h"
 #include "../ClangTidyModuleRegistry.h"
+#include "ImplementationInNamespaceCheck.h"
 #include "RestrictSystemLibcHeadersCheck.h"
 
 namespace clang {
@@ -18,6 +19,8 @@
 class LLVMLibcModule : public ClangTidyModule {
 public:
   void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
+    CheckFactories.registerCheck<ImplementationInNamespaceCheck>(
+        "llvmlibc-implementation-in-namespace");
     CheckFactories.registerCheck<RestrictSystemLibcHeadersCheck>(
         "llvmlibc-restrict-system-libc-headers");
   }