When PARALLEL_MAKE is used with the current blktrace Makefile, the
btreplay and btrecord object files can end up being built multiple
times in parallel, which occasionally causes the linker to pick up the
object files in intermediate and seemingly corrupt states, and causes
the spurious link errors in the bug report.
This fix restricts the recursive btreplay invocations to building only
btreplay or btrecord as appropriate, not both.
Signed-off-by: Tom Zanussi <tom.zanussi@intel.com>
