Cannot compile with older GCCs

[coderforlife]

Since the flag -std=c++11 is used to compile the Cython modules older GCCs are not supported. For example, rocce needs -std=c++0x instead.

Additionally there are the following warnings which should be checked to see if they exist on newer GCCs or not:

cc1plus: warning: command line option "-Wstrict-prototypes" is valid for Ada/C/ObjC but not for C++
segtools/pysegtools/general/cython/npy_helper.h:216: warning: expected [error|warning|ignored] after '#pragma GCC diagnostic'
segtools/pysegtools/general/cython/npy_helper.h:234: warning: expected [error|warning|ignored] after '#pragma GCC diagnostic'

The _label.pyx file has several additional warnings related to the npy_helper:

pysegtools/images/filters/_label.cpp:2299: warning: invalid access to non-static data member 'half::raw'  of NULL object
pysegtools/images/filters/_label.cpp:2299: warning: (perhaps the 'offsetof' macro was used incorrectly)
pysegtools/images/filters/_label.cpp:2308: warning: invalid access to non-static data member 'complex<float>::R'  of NULL object
pysegtools/images/filters/_label.cpp:2308: warning: (perhaps the 'offsetof' macro was used incorrectly)
pysegtools/images/filters/_label.cpp:2309: warning: invalid access to non-static data member 'complex<float>::I'  of NULL object
pysegtools/images/filters/_label.cpp:2309: warning: (perhaps the 'offsetof' macro was used incorrectly)
pysegtools/images/filters/_label.cpp:2315: warning: invalid access to non-static data member 'complex<double>::R'  of NULL object
pysegtools/images/filters/_label.cpp:2315: warning: (perhaps the 'offsetof' macro was used incorrectly)
pysegtools/images/filters/_label.cpp:2316: warning: invalid access to non-static data member 'complex<double>::I'  of NULL object
pysegtools/images/filters/_label.cpp:2316: warning: (perhaps the 'offsetof' macro was used incorrectly)
pysegtools/images/filters/_label.cpp:2322: warning: invalid access to non-static data member 'complex<long double>::R'  of NULL object
pysegtools/images/filters/_label.cpp:2322: warning: (perhaps the 'offsetof' macro was used incorrectly)
pysegtools/images/filters/_label.cpp:2323: warning: invalid access to non-static data member 'complex<long double>::I'  of NULL object
pysegtools/images/filters/_label.cpp:2323: warning: (perhaps the 'offsetof' macro was used incorrectly)

But none of these should effect common usage.