WIP: first working version with newlib + nacl

Problems:
1. User has to name his executable well to avoid errors with google's tools
2. glib not supported
3. Variant not really set correctly (object dir does not state which one we build)
4. All variants should be built?
aux outputs: lookup by node keyword rather than node label

Program's label is Program $(@) which meant we looked up the AUX_FILES_
environment variables incorrectly.

By switching to self.Keyword we lookup AUX_FILES_PROGRAM and correctly
detect the output files. Which are thus correctly cleaned up.

AUX_FILES_SHAREDLIB is renamed to AUX_FILES_SHAREDLIBRARY [API Change]
minor cosmetic change
added syntax nodes for NaCL

NaCL Manifest will produce a .nmf file from its dependencies (which must be Program(s))
allow building x86_32 or x86_64