gn: declare use_debug_fission and use_gold as a build arguments

build/config/compiler/BUILD.gn

 # Copyright (c) 2013 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.
 
 import("//build/config/android/config.gni")
 if (cpu_arch == "arm") {
   import("//build/config/arm.gni")
 }
 if (is_posix) {
   import("//build/config/gcc/gcc_version.gni")
@@ skipping 15 matching lines @@
   # Compile in such a way as to enable profiling of the generated code. For
   # example, don't omit the frame pointer and leave in symbols.
   enable_profiling = false
 
   # Compile in such a way as to make it possible for the profiler to unwind full
   # stack frames. Setting this flag has a large effect on the performance of the
   # generated code than just setting profiling, but gives the profiler more
   # information to analyze.
   # Requires profiling to be set to true.
   enable_full_stack_frames_for_profiling = false
-}
 
-use_gold = is_linux && cpu_arch == "x64"
+  # Use gold for linking on 64-bit Linux only (on 32-bit it runs out of
+  # address space, and it doesn't support cross-compiling).
+  use_gold = is_linux && cpu_arch == "x64"
 
-if (!is_win) {
-  # linux_use_debug_fission: whether to use split DWARF debug info
+  # use_debug_fission: whether to use split DWARF debug info
   # files. This can reduce link time significantly, but is incompatible
   # with some utilities such as icecc and ccache. Requires gold and
   # gcc >= 4.8 or clang.
   # http://gcc.gnu.org/wiki/DebugFission
-  use_debug_fission = use_gold && linux_use_bundled_binutils && !use_ccache
+  use_debug_fission =
+      !is_win && use_gold && linux_use_bundled_binutils && !use_ccache
 }
 
 # default_include_dirs ---------------------------------------------------------
 #
 # This is a separate config so that third_party code (which would not use the
 # source root and might have conflicting versions of some headers) can remove
 # this and specify their own include paths.
 config("default_include_dirs") {
   include_dirs = [
     "//",
@@ skipping 246 matching lines @@
     ]
   }
 
   # Linux-specific compiler flags setup.
   # ------------------------------------
   if (is_linux) {
     cflags += [ "-pthread" ]
     ldflags += [ "-pthread" ]
   }
   if (use_gold) {
-    # Use gold for linking on 64-bit Linux only (on 32-bit it runs out of
-    # address space, and it doesn't support cross-compiling).
     gold_path = rebase_path("//third_party/binutils/Linux_x64/Release/bin",
                             root_build_dir)
     ldflags += [
       "-B$gold_path",
 
       # Newer gccs and clangs support -fuse-ld, use the flag to force gold
       # selection.
       # gcc -- http://gcc.gnu.org/onlinedocs/gcc-4.8.0/gcc/Optimize-Options.html
       "-fuse-ld=gold",
 
@@ skipping 662 matching lines @@
       cflags += [ "-gsplit-dwarf" ]
     }
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }