-If you want to add to, not replace, compile flags, you can use OURDEFS:
- ./configure OURDEFS='-Wextra -Wno-sign-compare'
+If you wish to add options that are only used at compile time instead of
+link time, you can use the CPPFLAGS variable:
+ ./configure CPPFLAGS='-Wextra -Wno-sign-compare'