[NaCl SDK] Add realpath(3) implementation.

native_client_sdk/src/tests/nacl_io_test/example.dsc

 {
   'TOOLS': ['bionic', 'newlib', 'glibc', 'pnacl', 'linux'],
   'SEL_LDR': True,
 
   'TARGETS': [
     {
       'NAME' : 'nacl_io_test',
       'TYPE' : 'main',
       'SOURCES' : [
         'dev_fs_for_testing.h',
@@ skipping 35 matching lines @@
         'kernel_proxy_test.cc',
         'kernel_wrap_test.cc',
         'main.cc',
         'mem_fs_node_test.cc',
         'mock_fs.cc',
         'mock_fs.h',
         'mock_kernel_proxy.h',
         'mock_node.cc',
         'mock_node.h',
         'mock_util.h',
+        'syscalls_test.cc',
         'path_test.cc',
         'pepper_interface_mock.cc',
         'pepper_interface_mock.h',
         'socket_test.cc',
         'tty_test.cc',
       ],
       'DEPS': ['ppapi_simple', 'nacl_io'],
       # Order matters here: gtest has a "main" function that will be used if
       # referenced before ppapi.
       'LIBS': ['ppapi_simple', 'gmock', 'nacl_io', 'ppapi_cpp', 'ppapi', 'gtest', 'pthread'],
       'INCLUDES': ["."],
       'CXXFLAGS': ['-Wno-sign-compare'],
     }
   ],
   'DATA': [
     'example.js'
   ],
   'DEST': 'tests',
   'NAME': 'nacl_io_test',
   'TITLE': 'NaCl IO test',
 }