debug 1.8.0 fails to install/compile on truffleruby-dev, RBASIC(strio)->flags

[eregon]

$ gem i debug
Fetching debug-1.8.0.gem
Building native extensions. This could take a while...
ERROR:  Error installing debug:
	ERROR: Failed to build gem native extension.

    current directory: /home/eregon/.rubies/truffleruby-dev/lib/gems/gems/debug-1.8.0/ext/debug
/home/eregon/.rubies/truffleruby-dev/bin/ruby extconf.rb
checking for rb_iseq_parameters(NULL, 0) in VALUE rb_iseq_parameters(void *, int is_proc);... no
checking for rb_iseq_code_location(NULL, NULL, NULL, NULL, NULL) in void rb_iseq_code_location(void *, int *first_lineno, int *first_column, int *last_lineno, int *last_column);... no
checking for rb_iseq_type(NULL) in VALUE rb_iseq_type(void *);... no
creating Makefile

current directory: /home/eregon/.rubies/truffleruby-dev/lib/gems/gems/debug-1.8.0/ext/debug
make DESTDIR\= sitearchdir\=./.gem.20231128-3846727-u2vz7s sitelibdir\=./.gem.20231128-3846727-u2vz7s clean

current directory: /home/eregon/.rubies/truffleruby-dev/lib/gems/gems/debug-1.8.0/ext/debug
make DESTDIR\= sitearchdir\=./.gem.20231128-3846727-u2vz7s sitelibdir\=./.gem.20231128-3846727-u2vz7s
compiling debug.c
compiling iseq_collector.c
iseq_collector.c: In function ‘imemo_type’:
iseq_collector.c:18:13: error: implicit declaration of function ‘RBASIC’ [-Werror=implicit-function-declaration]
   18 |     return (RBASIC(imemo)->flags >> FL_USHIFT) & imemo_mask;
      |             ^~~~~~
iseq_collector.c:18:26: error: invalid type argument of ‘->’ (have ‘int’)
   18 |     return (RBASIC(imemo)->flags >> FL_USHIFT) & imemo_mask;
      |                          ^~
iseq_collector.c: In function ‘iseq_i’:
iseq_collector.c:39:22: error: invalid type argument of ‘->’ (have ‘int’)
   39 |         if (RBASIC(v)->flags) {
      |                      ^~

This is expected since #3118.
Fix for upstream in ruby/debug#1039