Libraries aMule will use to build:
wxWidgets 2.4.2
GTK Not detected
Man this is weird, looks like you are not missing wxGTK, you are missing gtk itself

Just joking, you are probably missing a devel package of gtk. Look (and post yours after me):
$ rpm -qa | grep -i gtk | grep -i devel
gtkhtml-devel-1.1.9-10
pygtk2-devel-2.4.0-1
gtk+-devel-1.2.10-33.5.3.kde
gtk2-devel-2.4.14-2.fc3
In your case, as you are using wxGTK-2.4.2, look for gtk+-devel. If not installed, please install it.
Cheers!