benchmarks: run with clang to workaround build failure with gcc
benchmarks: run with clang to workaround build failure with gcc

Change-Id: Ic56bda0bd6f8a0927fdab4bbe96b13c9bb3f9de2
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/3899
Tested-by: jenkins
Reviewed-by: Todd Lipcon <2c763d726a8c2f6afda9be7e0e56a2caa6bb5e6b@cloudera.com>

helifu/kudu,cloudera/kudu,helifu/kudu,InspurUSA/kudu,helifu/kudu,EvilMcJerkface/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,InspurUSA/kudu,helifu/kudu,andrwng/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,helifu/kudu,helifu/kudu,helifu/kudu,cloudera/kudu,andrwng/kudu,andrwng/kudu,helifu/kudu,InspurUSA/kudu,InspurUSA/kudu,andrwng/kudu,EvilMcJerkface/kudu,helifu/kudu,InspurUSA/kudu,cloudera/kudu,EvilMcJerkface/kudu,andrwng/kudu,EvilMcJerkface/kudu,cloudera/kudu,EvilMcJerkface/kudu,cloudera/kudu,andrwng/kudu,cloudera/kudu,cloudera/kudu,cloudera/kudu,andrwng/kudu,InspurUSA/kudu,InspurUSA/kudu,andrwng/kudu,cloudera/kudu,EvilMcJerkface/kudu,andrwng/kudu,EvilMcJerkface/kudu