Create test case for when the enum or the union comes from the std namespace but

not a system header.

Author: tigbr

clang-tools-extra/test/clang-tidy/checkers/bugprone/Inputs/tagged-union-member-count/stdnamespace.h

@@ -0,0 +1,12 @@
+#define __SIZEOF_PTHREAD_MUTEX_T 40
+
+namespace std {
+  typedef union {
+    struct __pthread_mutex_s {
+      int __lock;
+      unsigned int __count;
+    } __data;
+    char __size[__SIZEOF_PTHREAD_MUTEX_T];
+    long int __align;
+  } pthread_mutex_t;
+};

clang-tools-extra/test/clang-tidy/checkers/bugprone/tagged-union-member-count.cpp

@@ -1,4 +1,5 @@
 // RUN: %check_clang_tidy -std=c++98-or-later %s bugprone-tagged-union-member-count %t -- -- \
+// RUN: -I%S/Inputs/tagged-union-member-count \
 // RUN: -isystem %S/Inputs/tagged-union-member-count/system
 // Test check with C++ features
 
@@ -322,3 +323,13 @@ struct SystemTypedefedUnionDataMemberShouldBeIgnored {
     MyEnum
   } EnumField;
 };
+
+// Filter when union or enum comes from the std namespace but not a system header
+#include "stdnamespace.h"
+
+struct StdNameSpaceUnionDataMemberShouldBeIgnored {
+  std::pthread_mutex_t Mutex;
+  enum {
+    MyEnum
+  } EnumField;
+};