encperf: change % to %% in printf format
GCC lets this slide, but other compilers (clang) complain about using % rather
than %% to print a literal % character.
diff --git a/tests/encperf.cxx b/tests/encperf.cxx
index 2064496..31d7c73 100644
--- a/tests/encperf.cxx
+++ b/tests/encperf.cxx
@@ -442,7 +442,7 @@
   sort(dev, runCount);
   meddev = dev[runCount / 2];
 
-  printf("CPU time: %g s (+/- %g %)\n", median, meddev);
+  printf("CPU time: %g s (+/- %g %%)\n", median, meddev);
   printf("Encoded bytes: %lld\n", bytes);
   printf("Raw equivalent bytes: %lld\n", equivalent);
   printf("Ratio: %g\n", ratio);