Ensure Errno.{handle,handle_errno} are never called with errno=0

(cherry picked from commit 20c93ab)

Author: eregon

src/main/java/org/truffleruby/core/VMPrimitiveNodes.java

@@ -529,4 +529,15 @@ protected long endHash(long hash) {
 
     }
 
+    @Primitive(name = "should_not_reach_here")
+    public abstract static class ShouldNotReachHereNode extends PrimitiveArrayArgumentsNode {
+
+        @Specialization(guards = "libString.isRubyString(message)")
+        protected Object shouldNotReachHere(Object message,
+                @CachedLibrary(limit = "2") RubyStringLibrary libString) {
+            throw CompilerDirectives.shouldNotReachHere(libString.getJavaString(message));
+        }
+
+    }
+
 }

src/main/ruby/truffleruby/core/errno.rb

@@ -43,13 +43,13 @@ module Errno
   # Unlike rb_sys_fail(), handle does not raise an exception if errno is 0.
   def self.handle(additional = nil)
     err = errno
-    return if err == 0
+    Primitive.should_not_reach_here('Errno.handle called but errno was 0') if err == 0
 
     raise SystemCallError.new(additional, err)
   end
 
   def self.handle_errno(errno)
-    return if errno == 0
+    Primitive.should_not_reach_here('Errno.handle_errno called but errno was 0') if errno == 0
 
     raise SystemCallError.new(nil, errno)
   end