Make complex.h play nice with C

llvm-svn: 109791
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: a8e3da215c5367b6f58f428fe32a346dd39454f4
diff --git a/include/complex.h b/include/complex.h
index ae260c2..95aaa71 100644
--- a/include/complex.h
+++ b/include/complex.h
@@ -18,8 +18,16 @@
 
 */
 
+#ifdef __cplusplus
+
 #include <ccomplex>
 
+#else
+
+#include_next <complex.h>
+
+#endif
+
 #pragma GCC system_header
 
 #endif  // _LIBCPP_COMPLEX_H