introduce -optimized-tools option

instead of building host tools always in debug mode, follow the overall
build type, and provide an option to override it.

this supersedes the pre-existing -optimized-qmake option.
however, that option never existed in the windows configure, and this
legacy continues as far as qmake is concerned (msvc builds of qmake are
always somewhat optimized, but not mingw builds).

Change-Id: I42e7ef1a481840699a8dffff13fec2626af19cc6
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>