log4cxx: new version and fix for c++11 (#26480)
log4cxx: new version and fix for c++11 (#26480)

* Add version 0.12.1

* Add variant to build with C++11 standard

build with c++11 standard requires boost threads, and needs explicit setting of
CMAKE_CXX_STANDARD
LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack