[GN]: Add asmflags

tools/gn/misc/vim/syntax/gn.vim

 " Copyright 2014 The Chromium Authors. All rights reserved.
 " Use of this source code is governed by a BSD-style license that can be
 " found in the LICENSE file.
 "
 " gn.vim: Vim syntax file for GN.
 "
 " Quit when a (custom) syntax file was already loaded
 "if exists("b:current_syntax")
   "finish
 "endif
@@ skipping 23 matching lines @@
 syn keyword     gnFunctions foreach get_label_info get_path_info
 syn keyword     gnFunctions get_target_outputs getenv import print
 syn keyword     gnFunctions process_file_template read_file rebase_path
 syn keyword     gnFunctions set_default_toolchain set_defaults
 syn keyword     gnFunctions set_sources_assignment_filter template tool
 syn keyword     gnFunctions toolchain toolchain_args write_file
 hi def link     gnFunctions         Macro
 
 " Variables
 syn keyword     gnVariable all_dependent_configs allow_circular_includes_from
-syn keyword     gnVariable args cflags cflags_c cflags_cc cflags_objc
+syn keyword     gnVariable args asmflags cflags cflags_c cflags_cc cflags_objc
 syn keyword     gnVariable cflags_objcc check_includes complete_static_lib
 syn keyword     gnVariable configs data data_deps defines depfile deps
 syn keyword     gnVariable forward_dependent_configs_from include_dirs inputs
 syn keyword     gnVariable ldflags lib_dirs libs output_extension output_name
 syn keyword     gnVariable outputs public public_configs public_deps script
 syn keyword     gnVariable sources testonly visibility
 hi def link     gnVariable          Keyword
 
 " Strings
 syn region          gnString start=+L\="+ skip=+\\\\\|\\"+ end=+"+ contains=@Spell
@@ skipping 17 matching lines @@
 "syn match gnOperator /-=/
 "syn match gnOperator /\s>\s/
 "syn match gnOperator /\s<\s/
 "syn match gnOperator /\s+\s/
 "syn match gnOperator /\s-\s/
 "hi def link     gnOperator          Operator
 
 syn sync minlines=500
 
 let b:current_syntax = "gn"