Don't create build_script_log file with --dry-run flag

(cherry picked from commit f6d04a0)

Author: shahmishal

utils/build-script

@@ -1378,10 +1378,11 @@ def main_normal():
     # Create build directory.
     shell.makedirs(invocation.workspace.build_root)
 
-    # Create .build_script_log.
-    build_script_log = os.path.join(invocation.workspace.build_root,
-                                    ".build_script_log")
-    open(build_script_log, 'w').close()
+    # Create .build_script_log
+    if not args.dry_run:
+        build_script_log = os.path.join(invocation.workspace.build_root,
+                                        ".build_script_log")
+        open(build_script_log, 'w').close()
 
     # Build ninja if required, which will update the toolchain.
     if args.build_ninja: