Update CXXFLAGS

See stan-dev/math#2257.

Author: hsbadr

R/build.R

@@ -50,7 +50,12 @@ tbbCxxFlags <- function() {
 
    if (dir.exists(Sys.getenv("TBB_INC"))) {
        TBB_INC <- asBuildPath(Sys.getenv("TBB_INC"))
-       flags <- paste0("-I", shQuote(TBB_INC))
+
+       if (file.exists(file.path(TBB_INC, "tbb", "version.h")))
+          flags <- paste0("-I", shQuote(TBB_INC), " -DTBB_INTERFACE_NEW")
+       } else {
+          flags <- paste0("-I", shQuote(TBB_INC))
+       }
    }
 
    flags