package/cegui: needs gcc >= 5

package/cegui: needs gcc >= 5

cegui needs gcc >= 5 since bump to current master in commit
352a8b3fe8b1d78073b1119369f10688e00bc859 and
https://github.com/cegui/cegui/commit/17f7f6156eb0ba903d5ae926e372b8c5c26d8c68
or the build will fail on:

/home/buildroot/autobuild/instance-1/output-1/build/cegui-00b4e1fe174da53b7ed726ab5970ba51bd5b5ee0/cegui/src/widgets/Spinner.cpp: In member function 'virtual CEGUI::String CEGUI::Spinner::getTextFromValue() const':
/home/buildroot/autobuild/instance-1/output-1/build/cegui-00b4e1fe174da53b7ed726ab5970ba51bd5b5ee0/cegui/src/widgets/Spinner.cpp:310:116: error: 'defaultfloat' is not a member of 'std'
             tmp << std::fixed << std::setprecision(d_precision) << d_currentValue << std::setprecision(defPrec) << std::defaultfloat;
                                                                                                                    ^

defaultfloat is not available before gcc 5 and
https://github.com/gcc-mirror/gcc/commit/c4b64f5bcac6f7d5e1ae7d3026a3e228fb8adbbd

Fixes:
 - http://autobuild.buildroot.org/results/006ce109980a76870d2347e53307082b36d9904a

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>