[gn] port 33a6ce1 (check-clang obj2yaml dep)

Author: nico

llvm/utils/gn/secondary/clang/test/BUILD.gn

@@ -201,6 +201,7 @@ group("test") {
     "//llvm/tools/llvm-readobj:symlinks",
     "//llvm/tools/llvm-readtapi:symlinks",
     "//llvm/tools/llvm-symbolizer:symlinks",
+    "//llvm/tools/obj2yaml",
     "//llvm/tools/opt",
     "//llvm/tools/yaml2obj",
     "//llvm/utils/FileCheck",