[gn build] Port b41b86a

Author: llvmgnsyncbot

llvm/utils/gn/secondary/clang/lib/Lex/BUILD.gn

@@ -11,6 +11,7 @@ static_library("Lex") {
     "HeaderMap.cpp",
     "HeaderSearch.cpp",
     "InitHeaderSearch.cpp",
+    "LexHLSLRootSignature.cpp",
     "Lexer.cpp",
     "LiteralSupport.cpp",
     "MacroArgs.cpp",

llvm/utils/gn/secondary/clang/unittests/Lex/BUILD.gn

@@ -17,6 +17,7 @@ unittest("LexTests") {
     "DependencyDirectivesScannerTest.cpp",
     "HeaderMapTest.cpp",
     "HeaderSearchTest.cpp",
+    "LexHLSLRootSignatureTest.cpp",
     "LexerTest.cpp",
     "ModuleDeclStateTest.cpp",
     "PPCallbacksTest.cpp",