Index: clang/lib/Lex/PPDirectives.cpp
===================================================================
--- clang/lib/Lex/PPDirectives.cpp
+++ clang/lib/Lex/PPDirectives.cpp
@@ -121,8 +121,21 @@
 
 static MacroDiag shouldWarnOnMacroDef(Preprocessor &PP, IdentifierInfo *II) {
   const LangOptions &Lang = PP.getLangOpts();
-  if (II->isReserved(Lang) != ReservedIdentifierStatus::NotReserved)
+  if (II->isReserved(Lang) != ReservedIdentifierStatus::NotReserved) {
+    static constexpr std::array<StringRef, 16> ReservedMacro = {
+        "_ATFILE_SOURCE",       "_BSD_SOURCE",    "_FILE_OFFSET_BITS",
+        "_FORTIFY_SOURCE",      "_GNU_SOURCE",    "_ISOC11_SOURCE",
+        "_ISOC95_SOURCE",       "_ISOC99_SOURCE", "_LARGEFILE64_SOURCE",
+        "_POSIX_C_SOURCE",      "_REENTRANT",     "_SVID_SOURCE",
+        "_THREAD_SAFE",         "_XOPEN_SOURCE",  "_XOPEN_SOURCE_EXTENDED",
+        "__STDC_FORMAT_MACROS",
+    };
+    if (std::binary_search(ReservedMacro.begin(), ReservedMacro.end(),
+                           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