uClibc: libc add isfdtype()

adopted from upstream
http://git.uclibc.org/uClibc/patch/?id=f22cca4722fa66e424562e69f4afa2bca0af871d

isfdtype(int fd, int fdtype) check whether a file descriptor fd is
of type fdtype, where the types are defined in stat(2).  It is
supported in glibc and BSD, and used by utilities such as acpid.

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>