Even after fixing #198027, the perf/vg_perf tool does not work for VPATH builds:

naesten@hydrogen:~/hacking/valgrind/inner% perl perf/vg_perf perf/

== 0 programs, 0 timings =================

naesten@hydrogen:~/hacking/valgrind/inner% perl perf/vg_perf ../perf/   
-- Running  tests in ../perf -------------------------------------------
vg_perf: './bigcode' not found or not a file (.)
naesten@hydrogen:~/hacking/valgrind/inner% 

The problem appears to be that vg_perf expects the passed directory to contain both the compiled test programs *and* the .vgperf files, but the test programs only show up in the build tree and the .vgperf files are only found in the source tree.