New Rtools sent to CRAN

I have just uploaded a new build of the Rtools33.exe installer to CRAN.  
It should appear on the mirrors within a day or two.

This installer includes the current build of gcc 4.9.3 from 
http://www.stat.ucla.edu/~jeroen/mingw-w64. It also includes
Jeroen's build of libicu55, which is necessary to build R.

The current R-devel build on CRAN should have the necessary changes to 
build R using this toolchain, 

Can you point to the specific changes (svn revision numbers) that were made to R-devel to facilitate this?

but the default is still the previous gcc 
4.6.3 toolchain; users should follow the instructions on 
https://github.com/rwinlib/r-base#readme to set up their systems to use it.

Please post any problems here or to me or Jeroen, as appropriate. We're 
hoping to be able to use this toolchain in R 3.3.x.

I installed this toolchain and the installer suggested adding the following to the beginning of my PATH:

c:\Rtools\bin;
c:\Rtools\gcc-4.6.3\bin;

Is that correct? Should it (also?) have suggested 

C:\Rtools\mingw_32\bin and C:\Rtools\mingw_64\bin?
Or does the new R know where to look for those? If so, how does it know?

Are the R-devel binaries available from CRAN being built with this toolchain?

I myself am not interested in building R from source with this toolchain but rather using it to build packages that have C/C++/Fortran code. 

Is there a way to tell which compiler is being used when I compile such a package?

R CMD config CC
just tells me "gcc -m64" it does not give the path to, or version of, the gcc that's being used.

I ran the Bioconductor builds overnight using this toolchain and recent R-devel and did not notice anything odd with packages containing native code, which means either the new toolchain is working perfectly (which is wonderful) or gcc-4.6.3 is still being used and maybe I need to do something to faciliate the use of gcc-4.9.3. Can you advise?

Thanks,
Dan