package/efl: fix build with poppler and gcc 5

package/efl: fix build with poppler and gcc 5

-std=c++11 is needed to avoid the following build failure with poppler
and gcc 5:

/home/naourr/work/instance-0/output-1/host/bin/../arm-buildroot-linux-uclibcgnueabi/sysroot/usr/include/poppler/cpp/poppler-page.h:40:37: note: C++11 'noexcept' only available with -std=c++11 or -std=gnu++11
/home/naourr/work/instance-0/output-1/host/bin/../arm-buildroot-linux-uclibcgnueabi/sysroot/usr/include/poppler/cpp/poppler-page.h:70:10: error: 'unique_ptr' in namespace 'std' does not name a template type
     std::unique_ptr<text_box_data> m_data;
          ^
Fixes:
 - http://autobuild.buildroot.org/results/3428b9017168db9239756dc06cdaa5ae004cab97

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