Required by bash-5.0 or else compilation fails:

 bashline.c:69:10: fatal error: readline/rlmbutil.h: No such file or directory
  #include <readline/rlmbutil.h>
           ^~~~~~~~~~~~~~~~~~~~~

--- readline-8.0/Makefile.in
+++ readline-8.0/Makefile.in
@@ -153,7 +153,7 @@
 CREATED_TAGS = TAGS tags
 
 INSTALLED_HEADERS = readline.h chardefs.h keymaps.h history.h tilde.h \
-		    rlstdc.h rlconf.h rltypedefs.h
+		    rlstdc.h rlconf.h rltypedefs.h rlmbutil.h
 
 OTHER_DOCS = $(srcdir)/CHANGES $(srcdir)/INSTALL $(srcdir)/README
 OTHER_INSTALLED_DOCS = CHANGES INSTALL README