[gn build] Port 56d45b0

Author: llvmgnsyncbot

llvm/utils/gn/secondary/lldb/source/Plugins/Language/CPlusPlus/BUILD.gn

@@ -34,6 +34,7 @@ static_library("CPlusPlus") {
     "LibCxxMap.cpp",
     "LibCxxQueue.cpp",
     "LibCxxRangesRefView.cpp",
+    "LibCxxSliceArray.cpp",
     "LibCxxSpan.cpp",
     "LibCxxTuple.cpp",
     "LibCxxUnorderedMap.cpp",