How does one make a bash "builtin" (shared loadable module) on cygwin?

[Rocky Bernstein]

I am trying to build a bash builtin on cygwin. Here's the error message I
get via automake/make:

$ make
gcc  -g -O2   -o set0.exe -shared set0-set0.o
set0-set0.o: In function `set0_builtin':
/tmp/bashdb/builtin/set0.c:46: undefined reference to `_builtin_error'
/tmp/bashdb/builtin/set0.c:47: undefined reference to `_builtin_usage'
/tmp/bashdb/builtin/set0.c:51: undefined reference to `_dollar_vars'
/tmp/bashdb/builtin/set0.c:52: undefined reference to `_xmalloc'
/tmp/bashdb/builtin/set0.c:52: undefined reference to `_dollar_vars'
/tmp/bashdb/builtin/set0.c:42: undefined reference to `_builtin_error'
/tmp/bashdb/builtin/set0.c:43: undefined reference to `_builtin_usage'
collect2: ld returned 1 exit status
make: *** [set0.exe] Error 1

Perhaps I need to tell cygwin that these symbols are supposed to be
undefined since they are part of bash?

Thanks for the help or suggestions,
   rocky