X87: use more suitable build flag

build/toolchain.gypi

 # Copyright 2013 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 274 matching lines @@
       }],
       ['v8_target_arch=="ia32"', {
         'defines': [
           'V8_TARGET_ARCH_IA32',
         ],
       }],  # v8_target_arch=="ia32"
       ['v8_target_arch=="x87"', {
         'defines': [
           'V8_TARGET_ARCH_X87',
         ],
-        'cflags': ['-mfpmath=387'],
-        'ldflags': ['-mfpmath=387'],
+        'cflags': ['-march=i586'],
       }],  # v8_target_arch=="x87"
       ['v8_target_arch=="mips"', {
         'defines': [
           'V8_TARGET_ARCH_MIPS',
         ],
         'variables': {
           'mipscompiler': '<!($(echo <(CXX)) -v 2>&1 | grep -q "^Target: mips" && echo "yes" || echo "no")',
         },
         'conditions': [
           ['mipscompiler=="yes"', {
@@ skipping 501 matching lines @@
                 'OptimizeReferences': '2',
                 'EnableCOMDATFolding': '2',
               },
             },
           }],  # OS=="win"
         ],  # conditions
       },  # Release
     },  # configurations
   },  # target_defaults
 }