Fix use of LOAD= with WantSystemLib()...

third_party/libxml/libxml.scons

 # Copyright 2008, Google Inc.
 # 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
@@ skipping 11 matching lines @@
 # OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 # SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 # LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 Import('env')
 
+if env.WantSystemLib('libxml'):
+    Return()
+
 env = env.Clone()
 
 env.Prepend(
     CPPPATH = [
         '$ICU38_DIR/public/common',
         '$ICU38_DIR/public/18n',
         '$ZLIB_DIR',
         'DerivedSources',
         'DerivedSources/include',
         'include',
     ],
-)
-
-env.Append(
     CPPDEFINES = [
         'U_STATIC_IMPLEMENTATION',
         'LIBXML_STATIC',
     ],
 )
 
 if env['PLATFORM'] == 'win32':
   env.Append(
       CCFLAGS = [
           '/TC',
@@ skipping 92 matching lines @@
               CONFIG_OPTIONS='compiler=msvc iconv=no icu=yes')
 elif env['PLATFORM'] == 'posix':
   config_files = [
       'config.h',
       'include/libxml/xmlversion.h',
       'xml2-config',
   ]
   for cf in config_files:
     result = env.Command('DerivedSources/' + cf, 'linux/' + cf,
                          Copy('$TARGET', '$SOURCE'))