Fix warning C4477 when building with MSVC without -Wv:18

Discovered by https://gerrit.libreoffice.org/c/core/+/163717

Like these:

 C:/lo/core/comphelper/source/windows/windows_process.cxx(254): warning C4477: 'wprintf' : format string '%s' requires an argument of type 'wchar_t *', but variadic argument 1 has type 'const void *'

Change-Id: Ia804bad18366d4f9422d72f3061c83cb07e92073
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/163783
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
diff --git a/comphelper/source/windows/windows_process.cxx b/comphelper/source/windows/windows_process.cxx
index 7588bae..8e7fd19 100644
--- a/comphelper/source/windows/windows_process.cxx
+++ b/comphelper/source/windows/windows_process.cxx
@@ -241,7 +241,7 @@ WinLaunchChild(const wchar_t *exePath,
    }
    else
    {
        LPVOID lpMsgBuf = nullptr;
        LPWSTR lpMsgBuf = nullptr;
        FormatMessageW(FORMAT_MESSAGE_ALLOCATE_BUFFER |
                       FORMAT_MESSAGE_FROM_SYSTEM |
                       FORMAT_MESSAGE_IGNORE_INSERTS,