Use -DFORTIFY_SOURCE=3 by appending it to CPPFLAGS directly instead of adding it indirectly to CFLAGS.
* Makefile (FORTIFY): Remove "-D_FORTIFY_SOURCE=3". (Fortify section/CPPFLAGS): New; append "-D_FORTIFY_SOURCE=3". (FEATURES): Remove. Contents moved to CPPFLAGS. (CPPFLAGS): New; append "-D_FILE_OFFSET_BITS=64". (CFLAGS): Do not use "$(FEATURES)".