Refactor dynamic_lib
Refactor dlsyms
Refactor dynamic_bs
Refactor xs_o and xs_c
Enable XSMULTI: multi *.xs under lib/ "just work"
Test, fix static build XS
t/xs.t even more pluggable with extra args to make calls
Break pure_all target into pure_nolink and linkext.
This allows breaking subdirs into subdirs_static and subdirs_dynamic.
This in turn allows building either static or dynamic when subdirs.
Add t/xs.t subdirsstatic to test.
Test, fix static XSMULTI