I'm nowhere close to being qualifed to write something
about
CXX/CFLAGS. Somebody else (not you) should provide a
paragraph
addressing those variables.
Read the documentation for gcc and make. They control how a program is compiled and can make a huge difference. The developer should know what the options do before they are set. Variables like CFLAGS and CXXFLAGS are often set or modified in a Makefile.
For qt based apps, it would also be helpful to read through the qmake manual as that generally is used, via a .pro file, to generate the Makefile for an application or library.
I have no problem with learning, but an RTFM response rather than helping is lame. :)
Darrell