Use -O9, tune for nocoma, assume at least a Pentium when generating code.

SConstruct

 # Copyright 2008 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 35 matching lines @@
       'CCFLAGS':      ['$DIALECTFLAGS', '$WARNINGFLAGS',
           '-fno-strict-aliasing'],
       'CXXFLAGS':     ['$CCFLAGS', '-fno-rtti', '-fno-exceptions'],
       'LIBS':         ['pthread']
     },
     'mode:debug': {
       'CCFLAGS':      ['-g', '-O0'],
       'CPPDEFINES':   ['ENABLE_DISASSEMBLER', 'DEBUG']
     },
     'mode:release': {
-      'CCFLAGS':      ['-O2']
+      'CCFLAGS':      ['-O9', '-mtune=nocona', '-march=pentium']
     },
     'wordsize:64': {
       'CCFLAGS':      ['-m32'],
       'LINKFLAGS':    ['-m32']
     }
   },
   'msvc': {
     'all': {
       'DIALECTFLAGS': ['/nologo'],
       'CCFLAGS':      ['$DIALECTFLAGS', '$WARNINGFLAGS'],
@@ skipping 63 matching lines @@
     'library:shared': {
       'CPPDEFINES':   ['BUILDING_V8_SHARED']
     }
   }
 }
 
 
 DTOA_EXTRA_FLAGS = {
   'gcc': {
     'all': {
-      'WARNINGFLAGS': ['-Werror']
+      'WARNINGFLAGS': ['-Werror', '-fno-strict-aliasing']
     }
   },
   'msvc': {
     'all': {
       'WARNINGFLAGS': ['/WX', '/wd4018', '/wd4244']
     }
   }
 }
 
 
@@ skipping 30 matching lines @@
   'gcc': {
     'all': {
       'LIBS': ['pthread'],
       'LIBPATH': ['.']
     },
     'wordsize:64': {
       'CCFLAGS':      ['-m32'],
       'LINKFLAGS':    ['-m32']
     },
     'mode:release': {
-      'CCFLAGS':      ['-O2']
+      'CCFLAGS':      ['-O2', '-mtune=nocona', '-march=pentium']
     },
     'mode:debug': {
       'CCFLAGS':      ['-g', '-O0']
     }
   },
   'msvc': {
     'all': {
       'CCFLAGS': ['/nologo'],
     },
     'library:shared': {
@@ skipping 340 matching lines @@
 # version of scons.  Also, there's a bug in some revisions that
 # doesn't allow this flag to be set, so we swallow any exceptions.
 # Lovely.
 try:
   SetOption('warn', 'no-deprecated')
 except:
   pass
 
 
 Build()