[license] Place all first party code under BSD license

Change-Id: I9ed09152ab36f85e2eb2bdf3691470476e4731f4

[build] Fix ABI stub generation for undefined symbols

Undefined symbols are in fact a part of the ABI for a DSO, an an
indirect fashion. The linker uses the presence of an undefined
symbol in a DSO to know that it needs to generate a dynamic
symbol table entry for that symbol when creating an executable
referring to that DSO. Without this, the symbol will not be
visible to the dynamic linker at runtime to satisfy the DSO's
reference.

Change-Id: Ic457440a70bc55760e027db56ffa8d6d2b1392db

[build] Generate DSO stubs for linking

The link-time ABI of a DSO is defined just by its symbol table.
There is no need to link against the actual DSO used at runtime.
Generate stub DSOs that change only when the ABI actually changes.
Link against those to reduce superfluous relinking. Install them
in the sysroot so the SDK sees only ABI and not implementation.

Change-Id: I080e2cf47ad60496c34eccf9ddb8ffc88238a97c