QtWebkit silently not built if gperf is not installed

We just noticed that the our installation of Qt 5.1.0 (final) does not include the qtwebkit module, although no error or warning messages at configure time or at the end of "make" occurred (I checked the configure output carefully).

Further testing showed that apparently the "qtwebkit" module is configured at build time only (1.5 hours into the build on my system) and if it fails, the user merely receives a short message embedded in serveral MB of console "make" output.

In this particular case (see attached log), qtwebkit was not built because "gperf" was not installed. Installing it, followed by "rm qtwebkit/Makefile ; make" fixes the problem.

I believe the configure script should check if gperf is installed and provide a note to the user, indicating that qtwebkit is not going to be built/installed. Alternatively, a warning at the end of "make" would be "good enough" already.

Ideally the whole configuration of qtwebkit should be performed when Qt is configured, not when "make" is called.

The attached log was made with RC2 of Qt 5.1.0, because that it what I have currently available on this system. The same problem was observed with 5.1.0 final (though I have not yet tested the fix there, but I believe there will be no difference).