xfsprogs: autoconf modernisation

xfsprogs: autoconf modernisation

Because apparently AC_TRY_COMPILE and AC_TRY_LINK has been
deprecated and made obsolete.

.....
configure.ac:164: warning: The macro `AC_TRY_COMPILE' is obsolete.
configure.ac:164: You should run autoupdate.
./lib/autoconf/general.m4:2847: AC_TRY_COMPILE is expanded from...
m4/package_libcdev.m4:68: AC_HAVE_GETMNTENT is expanded from...
configure.ac:164: the top level
configure.ac:165: warning: The macro `AC_TRY_LINK' is obsolete.
configure.ac:165: You should run autoupdate.
./lib/autoconf/general.m4:2920: AC_TRY_LINK is expanded from...
m4/package_libcdev.m4:84: AC_HAVE_FALLOCATE is expanded from...
configure.ac:165: the top level
.....

But "autoupdate" does nothing to fix this, so I have to manually do
these conversions:

	- AC_TRY_COMPILE -> AC_COMPILE_IFELSE
	- AC_TRY_LINK -> AC_LINK_IFELSE

because I have nothing better to do than fix currently working
code.

Also, running autoupdate forces the minimum pre-req to be autoconf
2.71 because it replaces other stuff...

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
[sandeen: use AC_PREREQ of 2.69 vs 2.71 to avoid bleeding edge]
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>