Some <termios.h> #define WRAP, undef it.
Grab the warnflags and stdflags from cflags [perl #122694].

They become $Config{ccwarnflags} and $Config{ccstdflags}.
Use sizeof() in UNUSED_ARG and UNUSED_VAR to avoid accessing the values.

The values might even be uninitialized in the case of PERL_UNUSED_VAR.