Reduce duplication among *printf-posix modules. * modules/mixin/printf-posix: New file. * modules/c-vasnprintf (Depends-on): Add it. Remove isnan*-nolibm, frexp*-nolibm, printf-frexp*, signbit, fpucw. * modules/dprintf-posix (Depends-on): Likewise. * modules/fprintf-posix (Depends-on): Likewise. * modules/snprintf-posix (Depends-on): Likewise. * modules/sprintf-posix (Depends-on): Likewise. * modules/unistdio/u16-u16-vasnprintf (Depends-on): Likewise. * modules/unistdio/u16-vasnprintf (Depends-on): Likewise. * modules/unistdio/u32-u32-vasnprintf (Depends-on): Likewise. * modules/unistdio/u32-vasnprintf (Depends-on): Likewise. * modules/unistdio/u8-u8-vasnprintf (Depends-on): Likewise. * modules/unistdio/u8-vasnprintf (Depends-on): Likewise. * modules/unistdio/ulc-vasnprintf (Depends-on): Likewise. * modules/vasnprintf-posix (Depends-on): Likewise. * modules/vasnwprintf-posix (Depends-on): Likewise. * modules/vasprintf-posix (Depends-on): Likewise. * modules/vdprintf-posix (Depends-on): Likewise. * modules/vfprintf-posix (Depends-on): Likewise. * modules/vsnprintf-posix (Depends-on): Likewise. * modules/vsprintf-posix (Depends-on): Likewise.