Linux: Add general autoconf macro for Linux kernel

Linux: Add general autoconf macro for Linux kernel

Add AC_CHECK_LINUX_BUILD() to do a standardised Linux build, which
takes a "checking" message, the autoconf variable to use to cache
the results, headers and code to run, preprocessor variable to
define, and a description of that variable.

Reviewed-on: http://gerrit.openafs.org/1854
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit a89d6b029d059d01b8bbfc18b9ee6e3f5a964b85)

Change-Id: I40730801f21bd058c66e475c4a5d2b67ace04cfb
[andersk@mit.edu: Remove reimplementation of existing check macros]
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
Reviewed-on: http://gerrit.openafs.org/3993
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Russ Allbery <rra@stanford.edu>
(cherry picked from commit 62c7e0b01e225708f525a9e6019fa11531b06aa4)