general:
- find libsamplerate's headers in the temporary sysroot instead of
digging in the source tree.
- use LIBADD where possible
lib/virtual_oss:
- centralize SHLIBDIR define
- centralize include path for internal headers
- don't try to find libsamplerate directly in .OBJDIR
No functional changes.
Reviewed by: christos
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D54704
Brooks Davis
373c72ad50