glibc/sysdeps/unix/sysv/linux/configure.in

sinclude(./aclocal.m4)dnl Autoconf lossage
GLIBC_PROVIDES dnl See aclocal.m4 in the top level source directory.
# Local configure fragment for sysdeps/unix/sysv/linux.

# On Linux, the default is to use libio instead of stdio.
test $stdio = default && stdio=libio

# Don't bother trying to generate any glue code to be compatible with the
# existing system library, because we are the only system library.
inhibit_glue=yes

AC_CACHE_CHECK(installed Linux kernel header files, libc_cv_linux201, [dnl
AC_TRY_COMPILE([#include <linux/version.h>],
[#if LINUX_VERSION_CODE < (2 *65536+ 0 *256+ 1) /* 2.0.1 */
eat flaming death
#endif],
	       libc_cv_linux201='2.0.1 or later',
	       libc_cv_linux201='TOO OLD!')])
if test "$libc_cv_linux201" != '2.0.1 or later'; then
  AC_MSG_ERROR([GNU libc requires kernel header files from Linux 2.0.1
or later to be installed before configuring.  The kernel header files
are found usually in /usr/include/asm and /usr/include/linux; make sure
these directories use files from Linux 2.0.1 or later.  This check uses
<linux/version.h>, so make sure that file was built correctly when
installing the kernel header files.])
fi