Android: Extra search directory to find make on windows

The sdk should set that extra directory, via the sdktool.

E. g. something like
sdktool addKeys android MakeExtraSearchDirectory QString:%DIRECTORY%

where %DIRECTORY% is the bin directory of the bundled mingw.
That is Tools\MinGW\bin for the qt sdk.

Also see:
Task-number: QTCREATORBUG-9297

Change-Id: I487c67b7fb704dd00cf5c6f4f647c8c4fbe8cd3d
Reviewed-by: Ray Donnelly <mingw.android@gmail.com>
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>