*printf: Fix for platforms where 'long double' == 'double'. * m4/printf.m4 (gl_PRINTF_INFINITE_LONG_DOUBLE): Require gl_LONG_DOUBLE_VS_DOUBLE. Don't blindly assume 80-bit 'long double'. * modules/dprintf-posix (Files): Add m4/math_h.m4. * modules/fprintf-posix (Files): Likewise. * modules/obstack-printf-posix (Files): Likewise. * modules/snprintf-posix (Files): Likewise. * modules/sprintf-posix (Files): Likewise. * modules/vasnprintf (Files): Likewise. * modules/vasnprintf-posix (Files): Likewise. * modules/vasprintf-posix (Files): Likewise. * modules/vdprintf-posix (Files): Likewise. * modules/vfprintf-posix (Files): Likewise. * modules/vsnprintf-posix (Files): Likewise. * modules/vsprintf-posix (Files): Likewise. * modules/unistdio/u8-vasnprintf (Files): Likewise. * modules/unistdio/u8-u8-vasnprintf (Files): Likewise. * modules/unistdio/u16-vasnprintf (Files): Likewise. * modules/unistdio/u16-u16-vasnprintf (Files): Likewise. * modules/unistdio/u32-vasnprintf (Files): Likewise. * modules/unistdio/u32-u32-vasnprintf (Files): Likewise. * modules/unistdio/ulc-vasnprintf (Files): Likewise.