Make sure the we use QtQuickCompiler only when we either have access
to the sources (internal gerrit repo) or the prebuilt binaries are available.

The internal-build class checks if we are working within The Qt Company network,
so we will also have access to the sources. Setting ENABLE_QTQUICKCOMPILER env
to "1" in local.conf has the same effect. Otherwise check if the prebuilt
binaries are available as installed by the Qt Online SDK.

Change-Id: I63b09ebabc96bb14b119ea7472a3fa7b10e5c2a8
Task-number: QTBUG-53052
Task-number: QTBUG-53216
Reviewed-by: Teemu Holappa <teemu.holappa@theqtcompany.com>