The configure script will automatically take certain environment variables such as CFLAGS, CXXFLAGS, and others and use them in your Qt environment by converting them to a QMAKE_CFLAGS or QMAKE_CXXFLAGS equivalent and then writing them to the .qmake.cache file so that they will be used by qmake. The LDFLAGS variable has no effect however because this will map to QMAKE_LDFLAGS, but the variable that qmake actually uses is QMAKE_LFLAGS so this value never gets added to Makefile.