add linux support for examples and libs

native_client_sdk/src/examples/geturl/example.dsc

 {
-  'TOOLS': ['newlib', 'glibc', 'pnacl', 'win'],
+  'TOOLS': ['newlib', 'glibc', 'pnacl', 'win', 'linux'],
   'TARGETS': [
     {
       'NAME' : 'geturl',
       'TYPE' : 'main',
       'SOURCES' : ['geturl.cc', 'geturl_handler.cc', 'geturl_handler.h'],
       'LIBS': ['ppapi_cpp', 'ppapi', 'pthread']
     }
   ],
   'DATA': ['geturl_success.html'],
   'DEST': 'examples',
   'NAME': 'geturl',
   'TITLE': 'Get URL',
   'DESC': """
 The Get URL example demonstrates fetching an URL and then displaying
 its contents.  Clicking the GetURL button will cause a geturl_success.html
 file to get loaded asynchronously, then displayed in a text box when the
 load completes.""",
   'INFO': 'Teaching focus: URL loading.'
 }