math/wxmaxima: fix build on GCC architectires
Use C++11 compiler:
CMake Error in src/CMakeLists.txt:
Target "wxmaxima" requires the language dialect "CXX11" (with compiler extensions), but CMake does not know the compile flags to use to enable it.
MFH: 2020Q3 (fix build blanket)2020Q3 (fix build blanket)