refactor(builtin): move pre-compiled object files to subdirectory

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(build): problem with reading LEAN_PATH on cygwin

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(builtin): dependency

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>