- CPPFLAGS gets -I and -D, CFLAGS gets everything else
- only save unique -I flags in CPPFLAGS; first instance takes precedence
- order non-system -I before system -I in CPPFLAGS
- LDFLAGS gets -L and other flags, LIBS gets -l and non-flags
- only save unique -L flags in LDFLAGS; first instance takes precedence
- order non-system -L before system -L in LDFLAGS
- only save unique -l flags in LIBS; last instance takes precedence
- add --with-[extra-]cflags and --with-[extra-]libs to all ./configures
Original: 7651d9511c759b9d145f9b88ed01c43c6f682add