diff --git a/clang/lib/Headers/stddef.h b/clang/lib/Headers/stddef.h
--- a/clang/lib/Headers/stddef.h
+++ b/clang/lib/Headers/stddef.h
@@ -98,7 +98,8 @@
 #endif /* defined(__need_NULL) */
 
 #if defined(__need_STDDEF_H_misc)
-#if __STDC_VERSION__ >= 201112L || __cplusplus >= 201103L
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) ||              \
+    (defined(__cplusplus) && __cplusplus >= 201103L)
 #include "__stddef_max_align_t.h"
 #endif
 #define offsetof(t, d) __builtin_offsetof(t, d)
diff --git a/clang/lib/Headers/stdint.h b/clang/lib/Headers/stdint.h
--- a/clang/lib/Headers/stdint.h
+++ b/clang/lib/Headers/stdint.h
@@ -91,6 +91,9 @@
  * defined if there exists an exact-width type of equal or greater width.
  */
 
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wmacro-redefined"
+
 #ifdef __INT64_TYPE__
 # ifndef __int8_t_defined /* glibc sys/types.h also defines int64_t*/
 typedef __INT64_TYPE__ int64_t;
@@ -857,5 +860,7 @@
 #define WINT_WIDTH       __WINT_WIDTH__
 #endif
 
+#pragma GCC diagnostic pop
+
 #endif /* __STDC_HOSTED__ */
 #endif /* __CLANG_STDINT_H */