Add a Subzero configuration to LLVM testsuite bot testing. x86-32 only.

buildbot/buildbot_pnacl_toolchain_tests.sh

Index: buildbot/buildbot_pnacl_toolchain_tests.sh
diff --git a/buildbot/buildbot_pnacl_toolchain_tests.sh b/buildbot/buildbot_pnacl_toolchain_tests.sh
index e1968264db980afc9e786d41aa55b5aefa3fa6b5..2ef20640fa0e04ba2aa6e66e4a30ab3c2bb991e5 100755
--- a/buildbot/buildbot_pnacl_toolchain_tests.sh
+++ b/buildbot/buildbot_pnacl_toolchain_tests.sh
@@ -203,6 +203,10 @@ tc-test-bot() {
     # world, all 4 combinations would be run.
     if [[ ${archset} =~ x86 ]]; then
       optset[2]="--opt O3f --opt O0b"
+      if [[ ${archset} == x86-32 ]]; then
+        # Run a Subzero -O2 test set on x86-32.
+        optset[3]="--opt O3f --opt O2b_sz"
+      fi
     fi
     for opt in "${optset[@]}"; do
       echo "@@@BUILD_STEP llvm-test-suite ${arch} ${opt} @@@"