Fix FXSYS_itoa() implementation.

pdfium.gyp

 {
   'variables': {
     'pdf_use_skia%': 0,
     'conditions': [
       ['OS=="linux"', {
         'bundle_freetype%': 0,
       }, {  # On Android there's no system FreeType. On Windows and Mac, only a
             # few methods are used from it.
         'bundle_freetype%': 1,
       }],
@@ skipping 701 matching lines @@
         'pdfium',
       ],
       'include_dirs': [
         '<(DEPTH)'
       ],
       'sources': [
         'core/src/fxcodec/codec/fx_codec_jpx_unittest.cpp',
         'core/src/fxcrt/fx_basic_bstring_unittest.cpp',
         'core/src/fxcrt/fx_basic_memmgr_unittest.cpp',
         'core/src/fxcrt/fx_basic_wstring_unittest.cpp',
+        'core/src/fxcrt/fx_system_unittest.cpp',
         'testing/fx_string_testhelpers.h',
         'testing/fx_string_testhelpers.cpp',
       ],
     },
     {
       'target_name': 'pdfium_embeddertests',
       'type': 'executable',
       'dependencies': [
         '<(DEPTH)/testing/gmock.gyp:gmock',
         '<(DEPTH)/testing/gtest.gyp:gtest',
@@ skipping 17 matching lines @@
         'testing/embedder_test.cpp',
         'testing/embedder_test.h',
         'testing/embedder_test_mock_delegate.h',
         'testing/embedder_test_timer_handling_delegate.h',
         'testing/fx_string_testhelpers.cpp',
         'testing/fx_string_testhelpers.h',
       ],
     },
   ],
 }