Fix build on C99 compilers
http://git.ghostscript.com/?p=ghostpdl.git;a=commitdiff;h=b24a4bd9bab156443c4667d4266e3deb43f933f7
--- base/stdpre.h.orig	2018-03-21 03:48:06.000000000 -0500
+++ base/stdpre.h	2018-03-29 23:11:41.000000000 -0500
@@ -95,6 +95,11 @@
 
 /* restrict is standard in C99, but not in all C++ compilers. */
 #if __STDC_VERSION__ == 199901L /* C99 */
+# if defined(HAVE_RESTRICT) && HAVE_RESTRICT==1
+#  define gs_restrict restrict
+# else /* defined(HAVE_RESTRICT) && HAVE_RESTRICT==1 */
+#  define gs_restrict
+# endif /* defined(HAVE_RESTRICT) && HAVE_RESTRICT==1 */
 #elif defined(_MSC_VER) && _MSC_VER >= 1500 /* MSVC 9 or newer */
 #define gs_restrict __restrict
 #elif __GNUC__ >= 3 /* GCC 3 or newer */