MSVC: default to separate debug info
MSVC: default to separate debug info

That's the VS default and what the user expects.

Change-Id: I857c44dbc478544d84d93512c66666acb37f37c6
Task-number: QBS-784
Reviewed-by: Christian Kandeler <3aa99dcdd3f0cac61fb81c2a11771c0cc2497607@theqtcompany.com>

qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,Distrotech/qbs,qt-labs/qbs,qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,gatzka/qt-labs-qbs,qt-labs/qbs,gatzka/qt-labs-qbs,gatzka/qt-labs-qbs,qtproject/qt-labs-qbs,Distrotech/qbs,gatzka/qt-labs-qbs,qtproject/qt-labs-qbs,Distrotech/qbs,Distrotech/qbs,qt-labs/qbs,Distrotech/qbs,qtproject/qt-labs-qbs,Distrotech/qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,Distrotech/qbs