Building a Qt module incorrectly inherits qtbase version numbers

When you build one of the other Qt modules, they incorrectly inherit qtbase's version.

Steps to reproduce:

1. Check out qtbase of a given version (for example, 5.0.2 or dev)
2. Build it
3. Check out qtsvg of a different version (for example, 5.0.1)
4. Build it

Note how it creates headers and a library for the wrong version.

For example, for qtbase=dev and qtsvg=stable:

rm -f libQt5Svg.so.5.1.0 libQt5Svg.so libQt5Svg.so.5 libQt5Svg.so.5.1
g++ -pipe -march=corei7-avx -Wl,-O1 -Wl,--as-needed -Wl,-z,relro -Wl,--no-undefined -Wl,-rpath,/home/thiago/obj/qt/qt5/qtbase/lib -shared -Wl,-soname,libQt5Svg.so.5 -o libQt5Svg.so.5.1.0 [other args]