I am building Qt 5.4 and I want to use my custom built `GCC` version which is different from the system one. I don't want to replace system `GCC` with my one. However, I don't see how can I alter the compiler absolute path that the Qt build system uses, as well as how to add custom flags. Usually open source libraries use `CXX` and `CXXFLAGS` variables to alter compiler absolute path and its options, but it looks like Qt build system ignores these variables.

Does Qt 5.4 build system have any options similar to common for GNU projects `CXX` and `CXXFLAGS`, as well as `LD` and `LDFLAGS`?