Conda: update gcc and isl error - gcc

Question

I have installed conda 4.3.22 and want to update conda gcc from 4.8.5 to 6.2.0. By using the following command I am getting an error because of the isl version. However, by trying to install a newer version of isl I am getting an error because of the gcc version. This is a rather dumb problem but I am not sure on how to get around it.
$ conda install -c salford_systems gcc-6=6.2.0
Fetching package metadata ...........
Solving package specifications:
PackageNotFoundError: Dependency missing in current linux-64 channels:
- gcc-6 6.2.0* -> isl >=0.17,<=0.17.1
$ conda install -c conda-forge isl=0.17.1
Fetching package metadata ...........
Solving package specifications: .
UnsatisfiableError: The following specifications were found to be in conflict:
- gcc -> isl >=0.10,<=0.14
- isl 0.17.1*
Use "conda info <package>" to see the dependencies for each package.
Edit 1:
As it was pointed out in the comments by darthbith, a combined command is not working and throws the following error:
$ conda install -c conda-forge -c salford_systems gcc-6=6.2.0 isl=0.17.1
Fetching package metadata .............
Solving package specifications: .
UnsatisfiableError: The following specifications were found to be in conflict:
- gcc -> isl 0.12.*
- gcc-6 6.2.0*
Use "conda info <package>" to see the dependencies for each package.
Do I understand it correct, that gcc and gcc-6 are different packages of which both require a different version of isl and thus leading to my problem? I only would need a newer version of gcc which supports GLIBCXX_3.4.21.
Thanks in advance.

Answer 1

I was able to solve my problem, thank you darthbith for helping me out.
Since gcc and gcc-6 are in fact two different packages, the solution was to delete gcc. After that, I had to update isl before I could install gcc-6. The commands used were:
conda uninstall gcc
conda install -c conda-forge isl=0.17.1
conda install -c salford_systems gcc-6=6.2.0