+ cpp => The C preprocessor command, normally not
+ given, as the build file defaults are
+ usually good enough.
+ cppflags => The C preprocessor flags.
+ defines => As an alternative, macro definitions may be
+ given here instead of in `cppflags'. If
+ given here, they MUST be as an array of the
+ string such as "MACRO=value", or just
+ "MACRO" for definitions without value.
+ includes => As an alternative, inclusion directories
+ may be given here instead of in `cppflags'.
+ If given here, the MUST be an array of
+ strings, one directory specification each.