Bazel bootstrapping: build an optimized binary

Pass "-c opt" when building bazel.

Fixes https://github.com/bazelbuild/bazel/issues/1830

--
MOS_MIGRATED_REVID=134307054
diff --git a/scripts/bootstrap/bootstrap.sh b/scripts/bootstrap/bootstrap.sh
index 14161ce..c656e15 100755
--- a/scripts/bootstrap/bootstrap.sh
+++ b/scripts/bootstrap/bootstrap.sh
@@ -34,11 +34,13 @@
   : ${BAZEL_ARGS:=--java_toolchain=//src/java_tools/buildjar:bootstrap_toolchain_jdk7 \
         --host_java_toolchain=//src/java_tools/buildjar:bootstrap_toolchain_jdk7 \
         --define JAVA_VERSION=1.7 --ignore_unsupported_sandboxing \
+        --compilation_mode=opt \
         "${EXTRA_BAZEL_ARGS:-}"}
 else
   : ${BAZEL_ARGS:=--java_toolchain=//src/java_tools/buildjar:bootstrap_toolchain \
         --host_java_toolchain=//src/java_tools/buildjar:bootstrap_toolchain \
         --strategy=Javac=worker --worker_quit_after_build --ignore_unsupported_sandboxing \
+        --compilation_mode=opt \
         "${EXTRA_BAZEL_ARGS:-}"}
 fi