Enable ccache for non-Unix target platforms

Remove the config.unix condition from the ccache feature. This enables
us to use ccache for non-Unix cross-builds like MinGW on Linux.

Change-Id: I3b108c2288754ad5dd05834e3d5a487c2da4ac00
Fixes: QTBUG-76681
Reviewed-by: Kai Koehne <kai.koehne@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

configure.json

@@ -1230,7 +1230,7 @@
         "ccache": {
             "label": "Using ccache",
             "autoDetect": false,
-            "condition": "config.unix && tests.ccache",
+            "condition": "tests.ccache",
             "output": [ "privateConfig" ]
         },
         "msvc_mp": {