pathname.rbinc conflicts with lib/pathname.rb in our test suite.

We can use `pathname.rb` after merging `lib/pathname.rb` to `pathname_builtin.rb`.

common.mk

@@ -1228,7 +1228,7 @@ BUILTIN_RB_SRCS = \
 		$(srcdir)/array.rb \
 		$(srcdir)/hash.rb \
 		$(srcdir)/kernel.rb \
-		$(srcdir)/pathname.rb \
+		$(srcdir)/pathname_builtin.rb \
 		$(srcdir)/ractor.rb \
 		$(srcdir)/symbol.rb \
 		$(srcdir)/timev.rb \
@@ -11247,7 +11247,7 @@ miniinit.$(OBJEXT): {$(VPATH)}numeric.rb
 miniinit.$(OBJEXT): {$(VPATH)}onigmo.h
 miniinit.$(OBJEXT): {$(VPATH)}oniguruma.h
 miniinit.$(OBJEXT): {$(VPATH)}pack.rb
-miniinit.$(OBJEXT): {$(VPATH)}pathname.rb
+miniinit.$(OBJEXT): {$(VPATH)}pathname_builtin.rb
 miniinit.$(OBJEXT): {$(VPATH)}prelude.rb
 miniinit.$(OBJEXT): {$(VPATH)}prism/ast.h
 miniinit.$(OBJEXT): {$(VPATH)}prism/diagnostic.h
@@ -13037,7 +13037,7 @@ pathname.$(OBJEXT): {$(VPATH)}missing.h
 pathname.$(OBJEXT): {$(VPATH)}onigmo.h
 pathname.$(OBJEXT): {$(VPATH)}oniguruma.h
 pathname.$(OBJEXT): {$(VPATH)}pathname.c
-pathname.$(OBJEXT): {$(VPATH)}pathname.rbinc
+pathname.$(OBJEXT): {$(VPATH)}pathname_builtin.rbinc
 pathname.$(OBJEXT): {$(VPATH)}ruby.h
 pathname.$(OBJEXT): {$(VPATH)}st.h
 pathname.$(OBJEXT): {$(VPATH)}subst.h

inits.c

@@ -99,7 +99,7 @@ rb_call_builtin_inits(void)
     BUILTIN(ast);
     BUILTIN(trace_point);
     BUILTIN(pack);
-    BUILTIN(pathname);
+    BUILTIN(pathname_builtin);
     BUILTIN(warning);
     BUILTIN(array);
     BUILTIN(hash);

pathname.c

@@ -1311,7 +1311,7 @@ path_f_pathname(VALUE self, VALUE str)
     return rb_class_new_instance(1, &str, rb_cPathname);
 }
 
-#include "pathname.rbinc"
+#include "pathname_builtin.rbinc"
 
 /*
  *