float: Work around <float.h> bugs on FreeBSD/x86, AIX with GCC, IRIX. * lib/float.in.h: Add workarounds for FreeBSD/x86, AIX with GCC, IRIX. * lib/float.c: New file. * m4/float_h.m4 (gl_FLOAT_H): Also handle FreeBSD, AIX, IRIX. Set REPLACE_FLOAT_LDBL. * modules/float (Files): Add lib/float.c. (configure.ac): Invoke AC_LIBOBJ. * doc/posix-headers/float.texi: Mention problems on FreeBSD, AIX, IRIX.