compile in static library with mkmf

[goldfita]

I have the following directory structure.

~/pyastman/ruby/ #ruby build dir
~/pyastman/ #code and library to wrap

The library is libast_man.a, which I want to link into my ruby
extension module at compile time. I'm not sure if this can be done
with a static library. It's not clear to me from the instructions. I
tried

require 'mkmf'
dir_config("ast_man")
have_library("ast_man","ast_connect")
create_makefile("rb_astman")

ruby extconf.rb --with-ast_man-lib=~/pyastman

It can't find the library. I tried various permutations on the names
as well. The next best thing would be to just tell it where the object
file is or even recompile the library. But I couldn't figure out how
to do this with mkmf either.

Thanks.