need to update cmake doc and auto tests

Yes, we have lots of changes about -fPIC things, cmake is also affected.

2.8.12 is requirement for this -fPIC change, and I think it only affects linux(or g++ compiler...?)

cmake doc and auto test need to be updated.

For example:(not only qtbase, but also other modules which has cmake auto test)
https://github.com/qtproject/qtdoc/blob/5.4/doc/src/development/cmake-manual.qdoc
https://github.com/qtproject/qtbase/blob/dev/tests/auto/cmake/CMakeLists.txt