[gn build] Port 4cabd1e

Author: llvmgnsyncbot

llvm/utils/gn/secondary/clang-tools-extra/clangd/unittests/BUILD.gn

@@ -70,6 +70,7 @@ unittest("ClangdTests") {
     "DumpASTTests.cpp",
     "ExpectedTypeTest.cpp",
     "FSTests.cpp",
+    "FeatureModulesRegistryTests.cpp",
     "FeatureModulesTests.cpp",
     "FileDistanceTests.cpp",
     "FileIndexTests.cpp",