ports-gcc doesn't have features.h so this fails; ports-gcc is newer than 6.0 anyway

Index: common/conf_post.h
--- common/conf_post.h.orig
+++ common/conf_post.h
@@ -73,11 +73,13 @@ typedef int ssize_t;
 #define REAL_GCC   __GNUC__ // probably
 #endif
 
+#if 0
 #ifdef REAL_GCC
 // Older gcc versions pretended to supply std::regex, but the resulting programs mostly crashed.
 #include <features.h>
 #if ! __GNUC_PREREQ(6,0)
 #define NO_STD_REGEX 1
+#endif
 #endif
 #endif