Eliminate need for build_config.h for OS_* defines.

build/SConscript.main

 # Copyright (c) 2006-2008 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 os
 import shutil
 import sys
 
 
 if sys.platform == 'win32':
@@ skipping 293 matching lines @@
     ],
 
     CCFLAGS = [
         '/nologo',
         '/errorReport:prompt',
     ],
 
     CPPDEFINES = [
         '_UNICODE',
         'UNICODE',
+        'OS_WIN',
     ],
 
 
     LIBS = [
         'advapi32.lib',
         'comdlg32.lib',
         'gdi32.lib',
         'kernel32.lib',
         'odbc32.lib',
         'odbccp32.lib',
@@ skipping 133 matching lines @@
     ],
     CCFLAGS = ['-m32', '-pthread', '-march=i686', '-fno-exceptions'],
     # GCC will generate ident directives with the GCC version. Accumulate
     # these all up and you end up with ~80K repeated in a .comment section.
     CCFLAGS_OPTIMIZED = ['-fno-ident'],
     CXXFLAGS = ['-Wall', '-Werror', '-march=i686'] + excluded_warnings,
     LINKFLAGS = ['-m32', '-pthread'],
 )
 
 linux_env.Replace(
+    CPPDEFINES = [
+        'OS_LINUX',
+        'OS_POSIX',
+    ],
+
     # Linking of large files uses lots of RAM, so serialize links
     # using the handy flock command from util-linux.
     LINK = 'flock $TARGET_ROOT/linker.lock ' + linux_env['LINK'],
 
     # We have several cases where archives depend on each other in a cyclic
     # fashion. (V8Bindings, libport and WebCore being the most significant
     # example.) Since the GNU linker does only a single pass over the archives
     # we need some extra trickery to deal with these unavoidable cycles. That
     # trickery is --start-group and --end-group (aka -( and -) ). That causes ld
     # to loop over the group until no more undefined symbols are found. In an
@@ skipping 188 matching lines @@
         '-Wnewline-eof',
         '-fvisibility=hidden',
         '-gdwarf-2',
         '-Wall',
         '-Wendif-labels',
         '-fstack-protector',
         '-fstack-protector-all',
     ],
     CPPDEFINES = [
         'DEBUG',
+        'OS_MACOSX',
+        'OS_POSIX',
     ],
 
     FRAMEWORKPATH = [
         mac_env.Dir('${TARGET_ROOT}'),
         '/System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks',
     ],
     FRAMEWORKS = [
         'AppKit',
         'ApplicationServices',
         'Foundation',
@@ skipping 152 matching lines @@
         'all_libraries',
         'all_languages',
         'all_programs',
         'all_test_programs',
     ], projects = [p],
     COMPONENT_VS_PROJECT_SCRIPT_PATH=(
         'cd $$(ProjectDir)/$VS_PROJECT_TO_MAIN_DIR && hammer.bat'),
 )
 
 # -------------------------------------------------------------------------