[PATCH] build: fix out-of-tree builds

[David Bremner]

Jani Nikula <jani at nikula.org> writes:
> ---
>
> David, does the perf test still work for you with these changes?

 make perf-test OPTIONS=--medium

runs the time tests, but then fails with

./performance-test/notmuch-memory-test --medium
make[1]: ./performance-test/notmuch-memory-test: Command not found
make[1]: *** [memory-test] Error 127
make[1]: Leaving directory `/home/bremner/software/upstream/notmuch'
make: *** [perf-test] Error 2

To be honest, the line 

TIME_TEST_SCRIPT :=$ $(srcdir)/$(dir)/notmuch-time-test

looks pretty strange to me, but that seems to be the one that is working