qt6_tool/Windows: Fix mis-detection of clang/g++ when in path by coincidence


Force cl.exe within a Visual Studio environment.

Change-Id: I1b73426718b213383243f926d8e33ad039e34105
Reviewed-by: Cristian Maureira-Fredes <cristian.maureira-fredes@qt.io>
commit0838a754346966c629c575158873fdc779e0060b
parentc29a3c2801d99b128ab68aab6a829d96c231d281
authorFriedemann Kleint <Friedemann.Kleint@qt.io>
committerFriedemann Kleint <Friedemann.Kleint@qt.io>
commit timeThu, 20 Feb 2025 08:43:29 +0000