gn build: Add a missing dependency from llvm/test to llvm-lit

check-llvm already listed llvm-lit as script which counts as a dep, so running
check-llvm worked fine, but `ninja -C out/gn llvm/test` didn't build llvm-lit
before if it wasn't already there.

llvm-svn: 352893

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

@@ -235,6 +235,7 @@ group("test") {
     "//llvm/utils/FileCheck",
     "//llvm/utils/TableGen:llvm-tblgen",
     "//llvm/utils/count",
+    "//llvm/utils/llvm-lit",
     "//llvm/utils/not",
 
     # llvm-config wants libgtest_main.a to exist at runtime when run as in