detect-toolchains: set qbs.architecture for MinGW

Task-number: QBS-446

Change-Id: I1c67c780dad5b5cc0444ede950809ae3cf71c67a
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>
detect-toolchains: set qbs.endianness for MinGW

Task-number: QBS-446

Change-Id: I4a1b88d1657e7ec71dc6e41e690f00dc606d3931
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>