I saw someplace someone specifying QMAKE_CFLAGS = -pipe. There wasn't any explanation beyond "to speed up build". How does it do that, and what are the alternative options?
The content of the variables QMAKE_CFLAGS (note:there are several variable with this prefix) will be forwarded to the C compiler, and doesn't have an influence on the qmake process.
Look at this SO thread to know what -pipe means for your compiler: When should I use GCC's -pipe option?