[gn build] Port 5e9eaf8

Author: llvmgnsyncbot

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

@@ -37,6 +37,7 @@ static_library("CPlusPlus") {
     "LibCxxSpan.cpp",
     "LibCxxTuple.cpp",
     "LibCxxUnorderedMap.cpp",
+    "LibCxxValarray.cpp",
     "LibCxxVariant.cpp",
     "LibCxxVector.cpp",
     "LibStdcpp.cpp",