R-devel does not set CXX1X, CXX1XSTD on compilers without full C++11 support. This is a departure from the current behavior of R 3.3.2, which does set these variables if the compiler has at least some support for C++11.
A reproducible example of the behavior can be found at https://github.com/jimhester/rocker/tree/master/r-devel/precise#readme along with instructions on reproducing. The repository directory can be checked out using git, or svn with
`svn co https://github.com/jimhester/rocker/trunk/r-devel/precise`.
A example case is ubuntu precise, which uses g++ 4.6.3. This compiler version does not have full support for C++11, but does have partial support. In previous R versions CXX1X and CXX1XSTD were set to `g++` and `-std=c++0x` respectively. With the current R-devel they are unset.
If a R package uses only supported C++11 features they can be successfully compiled with g++ 4.6.3 using R 3.3.2, but will fail to compile with R-devel.
Ideally we would like to retain the flags for partial support, while still setting e.g. `-std=c++11` if the compiler has full support for C++11.