Consolidated Ruby patches using major and minor versions

Previously we had to remember to apply specific patches for each
version of Ruby, and it was easy to forget. Let's just simplify this
by applying patches for the major and minor versions (e.g. 2.7, 3.0,
etc.).

patches/ruby/2.7/debug-segfault.patch

@@ -0,0 +1,25 @@
+diff --git a/class.c b/class.c
+index c866d1d727..37ff3c5ade 100644
+--- a/class.c
++++ b/class.c
+@@ -27,6 +27,7 @@
+ #include "ruby/st.h"
+ #include "constant.h"
+ #include "vm_core.h"
++#include "vm_debug.h"
+ #include "id_table.h"
+ #include <ctype.h>
+ 
+@@ -119,6 +120,12 @@ rb_class_foreach_subclass(VALUE klass, void (*f)(VALUE, VALUE), VALUE arg)
+     while (cur) {
+ 	VALUE curklass = cur->klass;
+ 	cur = cur->next;
++
++	if (curklass == 0) {
++		fprintf(stderr, "=== Detected NULL subclass:\n");
++		dp(curklass);
++	}
++
+ 	f(curklass, arg);
+     }
+ }