Extract build configuration into a separate header and move it to the base lib

BUILD.gn

 # 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.
 
 # TODO(jochen): These will need to be user-settable to support standalone V8
 # builds.
 v8_compress_startup_data = "off"
 v8_deprecation_warnings = false
 v8_enable_disassembler = false
 v8_enable_gdbjit = false
@@ skipping 875 matching lines @@
   if (v8_postmortem_support) {
     sources += [ "$target_gen_dir/debug-support.cc" ]
     deps += [ ":postmortem-metadata" ]
   }
 }
 
 source_set("v8_libbase") {
   visibility = ":*"  # Only targets in this file can depend on this.
 
   sources = [
+    "src/base/build_config.h",
     "src/base/macros.h",
   ]
 
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
   configs += [ ":internal_config", ":features", ":toolchain" ]
 }
 
 ###############################################################################
 # Executables
@@ skipping 21 matching lines @@
     ":v8_base",
     ":v8_nosnapshot",
   ]
 
   if (v8_compress_startup_data == "bz2") {
     libs = [ "bz2" ]
   }
 }
 
 }