I found another solution. The problematic package is fontconfig-devel. After uninstalling it, QT compiles just fine.
System: Red Hat Enterprise 5.4 Kernel 2.6.18-164.6.1.el5 on an x86_64
fontconfig-2.4.1-7.el5 (.i386 and x86_64)

Don't know if I need that devel, but I couldn't install fontconfig-2.4.2 (I'm quite new in Linux).