Enable valgrind support by default in Red Hat / Fedora package

[Ingvar Hagelund]

I got a request for enabling valgrind support by default in the RedHat/Fedora package, ie. add valgrind-devel to the build requirements. (bz#974270)

Is there any downside with just adding valgrind support to the RedHat/Fedora build?

How will jemalloc behave if valgrind support is compiled in, but valgrind is not installed at runtime?

Ingvar