Mute MSVC safety warnings

Botan:
C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xutility:2227:
warning: C4996: 'std::_Copy_impl': Function call with parameters that may be
unsafe - this call relies on the caller to check that the passed values are
correct. To disable this warning, use -D_SCL_SECURE_NO_WARNINGS. See
documentation on how to use Visual C++ 'Checked Iterators'

c:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\INCLUDE\xutility:2212:
see declaration of 'std::_Copy_impl'

D:\dev\qt-creator\src\libs\3rdparty\botan\botan.cpp:7248: see reference
to function template instantiation
'_OutIt std::copy<const Botan::u32bit*,T*>(_InIt,_InIt,_OutIt)' being compiled
with
[
    _OutIt=Botan::word *,
    T=Botan::word,
    _InIt=const Botan::u32bit *
]

CppTools:
C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xutility:2873:
warning: C4996: 'std::_Mismatch1': Function call with parameters that may be
unsafe - this call relies on the caller to check that the passed values are
correct. To disable this warning, use -D_SCL_SECURE_NO_WARNINGS. See
documentation on how to use Visual C++ 'Checked Iterators'

C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\INCLUDE\xutility:2856:
see declaration of 'std::_Mismatch1'

D:\dev\qt-creator\src\plugins\cpptools\symbolfinder.cpp:388: see reference to
function template instantiation 'std::pair<_Ty1,_Ty2>
std::mismatch<QString::const_iterator,QString::const_iterator>(_InIt1,_InIt1,_InIt2)'
being compiled
with
[
    _Ty1=QString::const_iterator,
    _Ty2=QString::const_iterator,
    _InIt1=QString::const_iterator,
    _InIt2=QString::const_iterator
]

Change-Id: I09a477e755c4555101b064271f10c08a69576e33
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
Reviewed-by: David Schulz <david.schulz@digia.com>
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>