Add kmeans benchmark to check rule

Expected to fail CI for clang, due to missing -ldl.  Also fails
for earlier versions of g++ (not covered by CI).

Makefile

@@ -19,3 +19,6 @@ install:: all
 
 bench bench_small bench_large::
 	@$(MAKE) -C benchmarks $@
+
+check::
+	@$(MAKE) -C benchmarks check

benchmarks/Makefile

@@ -4,3 +4,13 @@ DIRS := histogram kmeans linear_regression matrix_multiply \
 				sqlite-modified toy word_count
 
 include $(ROOT)/common.mk
+
+check::
+	@$(MAKE) -C kmeans
+	@$(RM) -f profile.coz
+	../coz run --- kmeans/kmeans
+	@grep -q "time=" profile.coz || { echo failure: valid profile.coz not generated; exit 1; }
+	@grep -q "throughput-point" profile.coz || { echo failure: throughput-point not found in profile; exit 1; }
+	@grep -q -P "samples\tlocation=" profile.coz || { echo failure: samples not found in profile; exit 1; }
+	@echo success: benchmark generated valid profile.coz
+	@$(RM) -f profile.coz