buildx: disable build speed for LC

Because LC has built sqlite3 which requires CGO with CGO_ENABLED=1, and
CGO can't support cross-compilation, this speed improvement can't used
in LC.

Signed-off-by: llhuii <liulinghui@huawei.com>

build/lc/Dockerfile

@@ -13,7 +13,10 @@
 # limitations under the License.
 
 # Add cross buildx improvement
-# _speed_buildx_for_go_
+# Because LC has built sqlite3 which requires CGO with CGO_ENABLED=1,
+# and CGO can't support cross compilation,
+# NO speed support for LC.
+# TODO: add https://musl.cc/ cross compilation tool
 FROM golang:1.14-alpine3.11 AS builder
 LABEL stage=builder