Fix reloading of patch files

(cherry picked from commit 37ddb4e9eb3aff7259ea60fe92c702f4bb5d3938)
Change-Id: I06c41eb802b0a3318da3ddfa72bd3575c02867fa
Task-number: QTCREATORBUG-13241
Reviewed-by: Jarek Kobus <jaroslaw.kobus@digia.com>
GccToolchain: Fix language variant detection

We got new C++ variants and need to adapt the logic to handle those.

Change-Id: I507628de8762f92894cbdb74244e915ea0ac4c64
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>