Rename the macro to make things shorter and more comprehensible. For
both meson and make builds, keep the old macro around for backward
compatibility.
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
The term "linuxapp" is a legacy one, but just calling the subdirectory
"linux" is just clearer for all concerned.
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>