Fix build on High Sierra and later
https://sourceforge.net/p/dc3dd/bugs/17/
https://lists.gnu.org/archive/html/bug-gnulib/2017-07/msg00057.html
--- lib/vasnprintf.c.orig	2012-11-06 06:42:58.000000000 -0600
+++ lib/vasnprintf.c	2017-11-28 04:10:15.000000000 -0600
@@ -4137,7 +4137,7 @@
 #endif
 		  *fbp = dp->conversion;
 #if USE_SNPRINTF
-# if !(__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 3) || ((defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__))
+# if !(__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 3) || (defined __APPLE__ && defined __MACH__) || ((defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__))
 		fbp[1] = '%';
 		fbp[2] = 'n';
 		fbp[3] = '\0';
