configure USE_LTO for clang on gitlab-ci

.gitlab-ci.yml

@@ -19,6 +19,11 @@ before_script:
       *-clang) ln -s /usr/lib/llvm4/lib/LLVMgold.so /usr/lib/LLVMgold.so;;
       *) ;;
     esac
+  - echo USE_RAMDISK=0 >> build.conf
+  - case "$CI_BUILD_NAME" in
+      *-clang) echo USE_LTO=1 >> build.conf;;
+      *) echo USE_LTO=0 >> build.conf;;
+    esac
 #==========  Stage build  ==========