make Rcpp_0.12.11 compile and installed on haiku-os

[armgong]

Today try install Rcpp on haiku-os , compile failed. then I modify two line in src/api.cpp line make Rcpp compile and install.
line 36 and line 275

     defined(__HAIKU__)

and RcppEigen also need modify install/include/unsupported/Eigen/src/SparseExtra/MatrixMaketIterator.h
line 196

    defined(__HAIKU__)

can we add this mod to the source ?

thanks

[eddelbuettel]

Please prepare a proper pull request.