Bug 1055655 - Fix warnings turned to errors by bug 1018288 found by mingw build. r=ted,jmathies

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extra : rebase_source : 2e1d8d0ae697515994b718634f8f8ae9b26b8d80
Bug 286355 - Fixed char16_t/wchar_t mismatch for mingw.

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extra : rebase_source : 285d1e36261ceab4cdf1be09024c4b7dbf907fd9