[gn build] Port a0f50d7

(cherry picked from commit 4612e48)

Author: llvmgnsyncbot

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

@@ -74,6 +74,7 @@ static_library("AST") {
     "Expr.cpp",
     "ExprCXX.cpp",
     "ExprClassification.cpp",
+    "ExprConcepts.cpp",
     "ExprConstant.cpp",
     "ExprObjC.cpp",
     "ExternalASTMerger.cpp",