Index: clang/lib/Lex/PPDirectives.cpp
===================================================================
--- clang/lib/Lex/PPDirectives.cpp
+++ clang/lib/Lex/PPDirectives.cpp
@@ -121,8 +121,49 @@
 
 static MacroDiag shouldWarnOnMacroDef(Preprocessor &PP, IdentifierInfo *II) {
   const LangOptions &Lang = PP.getLangOpts();
-  if (II->isReserved(Lang) != ReservedIdentifierStatus::NotReserved)
+  if (II->isReserved(Lang) != ReservedIdentifierStatus::NotReserved) {
+    // list from:
+    // - https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_macros.html
+    // - https://docs.microsoft.com/en-us/cpp/c-runtime-library/security-features-in-the-crt?view=msvc-160
+    // - man 7 feature_test_macros
+    // The list must be sorted for correct binary search.
+    static constexpr StringRef ReservedMacro[] = {
+        "_ATFILE_SOURCE",
+        "_BSD_SOURCE",
+        "_CRT_NONSTDC_NO_WARNINGS",
+        "_CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES",
+        "_CRT_SECURE_NO_WARNINGS",
+        "_FILE_OFFSET_BITS",
+        "_FORTIFY_SOURCE",
+        "_GLIBCXX_ASSERTIONS",
+        "_GLIBCXX_CONCEPT_CHECKS",
+        "_GLIBCXX_DEBUG",
+        "_GLIBCXX_DEBUG_PEDANTIC",
+        "_GLIBCXX_PARALLEL",
+        "_GLIBCXX_PARALLEL_ASSERTIONS",
+        "_GLIBCXX_SANITIZE_VECTOR",
+        "_GLIBCXX_USE_CXX11_ABI",
+        "_GLIBCXX_USE_DEPRECATED",
+        "_GNU_SOURCE",
+        "_ISOC11_SOURCE",
+        "_ISOC95_SOURCE",
+        "_ISOC99_SOURCE",
+        "_LARGEFILE64_SOURCE",
+        "_POSIX_C_SOURCE",
+        "_REENTRANT",
+        "_SVID_SOURCE",
+        "_THREAD_SAFE",
+        "_XOPEN_SOURCE",
+        "_XOPEN_SOURCE_EXTENDED",
+        "__STDCPP_WANT_MATH_SPEC_FUNCS__",
+        "__STDC_FORMAT_MACROS",
+    };
+    if (std::binary_search(std::begin(ReservedMacro), std::end(ReservedMacro),
+                           II->getName()))
+      return MD_NoWarn;
+
     return MD_ReservedMacro;
+  }
   StringRef Text = II->getName();
   if (II->isKeyword(Lang))
     return MD_KeywordDef;
Index: clang/test/Preprocessor/macro-reserved.c
===================================================================
--- clang/test/Preprocessor/macro-reserved.c
+++ clang/test/Preprocessor/macro-reserved.c
@@ -62,3 +62,6 @@
 #undef X__Y
 
 int x;
+
+#define _GNU_SOURCE          // no-warning
+#define __STDC_FORMAT_MACROS // no-warning