[gn build] [win] produce symbolized stack frames in release builds too

llvm/utils/gn/build/BUILD.gn

@@ -55,8 +55,13 @@ config("compiler_defaults") {
         "/Zi",
         "/FS",
       ]
-      ldflags += [ "/DEBUG" ]
     }
+
+    # Always ask the linker for a pdb. If the .obj files don't contain debug
+    # info, this will produce enough for function names in backtraces, and
+    # it doesn't slow down linking much.
+    ldflags += [ "/DEBUG" ]
+
     if (is_optimized) {
       cflags += [
         "/O2",