gn build: Merge r354365

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354411 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/gn/secondary/llvm/lib/Support/BUILD.gn b/utils/gn/secondary/llvm/lib/Support/BUILD.gn
index 9a5fbd9..1c20930 100644
--- a/utils/gn/secondary/llvm/lib/Support/BUILD.gn
+++ b/utils/gn/secondary/llvm/lib/Support/BUILD.gn
@@ -98,6 +98,7 @@
     "SHA1.cpp",
     "ScaledNumber.cpp",
     "ScopedPrinter.cpp",
+    "Signposts.cpp",
     "SmallPtrSet.cpp",
     "SmallVector.cpp",
     "SourceMgr.cpp",