stdioext: Add support for musl libc. * m4/fbufmode.m4 (gl_FUNC_FBUFMODE): Test whether __fbufsize exists. * lib/fbufmode.c (fbufmode): Add conditional code for musl. * m4/fseterr.m4: New file. * lib/fseterr.h (fseterr): Define as an alias of __fseterr if that function exists. * modules/fseterr (Files): Add m4/fseterr.m4. (configure.ac): Invoke gl_FUNC_FSETERR. Compile fseterr.c if __fseterr does not exist. (Makefile.am): Remove fseterr.c from lib_SOURCES. * lib/freadable.h: Update comment. * lib/fwritable.h: Update comment. * lib/freading.h: Update comment. * lib/fwriting.h: Update comment. * m4/freadahead.m4: New file. * lib/freadahead.h (freadahead): Define as an alias of __freadahead if that function exists. * modules/freadahead (Files): Add m4/freadahead.m4. (configure.ac): Invoke gl_FUNC_FREADAHEAD. Compile freadahead.c if __freadahead does not exist. (Makefile.am): Remove freadahead.c from lib_SOURCES. * m4/freadptr.m4: New file. * lib/freadptr.h (freadptr): Define as an alias of __freadptr if that function exists. * modules/freadptr (Files): Add m4/freadptr.m4. (configure.ac): Invoke gl_FUNC_FREADPTR. Compile freadptr.c if __freadptr does not exist. (Makefile.am): Remove freadptr.c from lib_SOURCES. * m4/freadseek.m4: New file. * lib/freadseek.c (freadptrinc): Use __freadptrinc if that function exists. * modules/freadseek (Files): Add m4/freadseek.m4. (configure.ac): Invoke gl_FUNC_FREADSEEK. * lib/fpurge.c (fpurge): Update comment. Reported by and with help from Rich Felker <dalias@aerifal.cx>.

# freadptr.m4 serial 1
dnl Copyright (C) 2012 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.

AC_DEFUN([gl_FUNC_FREADPTR],
[
  AC_CHECK_FUNCS_ONCE([__freadptr])
])