QNX has no libdl, but all the functions are in libc

Change-Id: I3f4b32eb8bbc0a35e817399516daa02de358575d
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>

config.tests/unix/libdl/libdl.pro

 SOURCES = libdl.cpp
 CONFIG -= qt dylib
-LIBS += -ldl
+!qnx: LIBS += -ldl