scons: Switch to c++17.

Change-Id: I90d121ab4dbf53f3bd30bcdb5f5101d9c7cdc437
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/45902
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed