luabridge uses static fn addresses to identify classes.
Windows uses different addresses for *identical* static functions
in libardour.dll and ardour.exe
This solves the issue by moving the all functions from a
header-only implementation into libardour.
uselib is no longer implicit (inherited by .use). This is still incomplete,
some uselibs for non-linux variants may be missing.
bld.is_defined("HAVE_XXX") also no longer works and will have to be
changed (I think to bld.env["HAVE_XXX"]) in countless places.
