create a profile per MSVC installation and per architecture

detect-toolchains will now create one profile per supported
architecture per found MSVC installation.

Task-number: QBS-404
Change-Id: I6ca569c312c31c39c49cfbfe5ffa638698fb90b2
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>