add linux support for examples and libs

native_client_sdk/src/examples/file_histogram/example.dsc

 {
-  'TOOLS': ['newlib', 'glibc', 'pnacl', 'win'],
+  'TOOLS': ['newlib', 'glibc', 'pnacl', 'win', 'linux'],
   'TARGETS': [
     {
       'NAME' : 'file_histogram',
       'TYPE' : 'main',
       'SOURCES' : ['file_histogram.cc'],
       'LIBS' : ['ppapi_cpp', 'ppapi', 'pthread']
     }
   ],
   'DEST': 'examples',
   'NAME': 'file_histogram',
   'TITLE': 'File Histogram.',
   'DESC': """
 The File Histogram example demonstrates prompting the user for a file,
 passing the file contents to NativeClient as a VarArrayBuffer, then drawing a
 histogram representing the contents of the file to a 2D square.
 """,
   'INFO': 'Teaching focus: VarArrayBuffer, 2D, File input.'
 }