Print out some warnings on unsupported build flags.

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 137 matching lines @@
 
     PERL                  = 'perl',
     PERL_INCLUDE_FLAG     = '-I ',
     PERL_INCLUDE_SUFFIX   = '',
     _PERL_INCLUDE_FLAGS   = ('${_concat(PERL_INCLUDE_FLAG, '
                              'PERL_INCLUDE_PATH, '
                              'PERL_INCLUDE_SUFFIX,'
                              '__env__, RDirs, TARGET, SOURCE)}'),
 )
 
-root_env['req_system_libs'] = ARGUMENTS.get('SYSTEM_LIBS', '').split(',')
+root_env['req_system_libs'] = []
+if 'SYSTEM_LIBS' in ARGUMENTS:
+  root_env['req_system_libs'] = ARGUMENTS['SYSTEM_LIBS'].split(',')
+  print "WARNING: Using system libs is not yet supported and may fail."
+  print "WARNING: You should only use this flag if you're willing to diagnose"
+  print "WARNING: and fix the inevitable link failures."
+
 root_env['_GYP'] = ARGUMENTS.get('GYP') and '_gyp' or ''
 
 def WantSystemLib(env, lib):
   """
   Return true if lib has been requested as a system library in SYSTEM_LIBS.
   """
   if lib not in env['all_system_libs']:
     env['all_system_libs'].append(lib)
   return (lib in env['req_system_libs'])
 root_env.AddMethod(WantSystemLib, "WantSystemLib")
@@ skipping 413 matching lines @@
 if ARGUMENTS.get('PROFILE') == '1':
   linux_env.Append(CCFLAGS=['-pg', '-g'])
   linux_env.Append(LINKFLAGS=['-pg'])
 
 # Build with symbols (useful for opt builds, for example) when SYMBOLS=1.
 if ARGUMENTS.get('SYMBOLS') == '1':
   linux_env.Append(CCFLAGS=['-g'])
 
 # Build shared libraries (useful for fast links) when SHARED=1.
 if ARGUMENTS.get('SHARED') == '1':
+  print "WARNING: The shared link frequently breaks and is unlikely to work."
+  print "WARNING: You should only use this flag if you're willing to diagnose"
+  print "WARNING: and fix the inevitable link failures."
   linux_env.Replace(COMPONENT_STATIC=False)
 
 # Build with system-provided NSS and GTK.
 if root_env['PLATFORM'] in ['linux', 'linux2', 'posix']:
   try:
     linux_env.ParseConfig('pkg-config --cflags --libs nss')
     linux_env.ParseConfig('pkg-config --cflags --libs gtk+-2.0')
     linux_env.ParseConfig('pkg-config --cflags --libs pangoft2')
   except OSError, e:
     print ('\n'
@@ skipping 289 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'),
 )
 
 # -------------------------------------------------------------------------