LU-16662 autoconf: fix configure test compile for CONFIG_KEYS

LU-16662 autoconf: fix configure test compile for CONFIG_KEYS

This fixes below configure error on Linux v5.19+:
$ ./configure --disable-server
...
checking whether to enable gss keyring backend... yes
checking if Linux kernel was built with CONFIG_KEYS in or as module...
no
configure: WARNING: GSS keyring backend requires that CONFIG_KEYS be
enabled in your kernel.
checking for keyctl_search in -lkeyutils... yes
configure: error: Cannot enable gss_keyring. See above for details.
$ grep CONFIG_KEYS -rn /boot/config-*
6884:CONFIG_KEYS=y

For in-tree IB support and without passing Linux src path when run
./configure, the LINUX_OBJ maybe just a soft link to O2IBPATH, they
are pointing to the same dir. E.g.:
O2IBPATH='/usr/src/kernels/6.1.8-3.0.0.7.oe1.aarch64'
LINUX_OBJ='/lib/modules/6.1.8-3.0.0.7.oe1.aarch64/build'
$ ls -l /lib/modules/6.1.8-3.0.0.7.oe1.aarch64/build
lrwxrwxrwx 1 root root 42 Feb  7 00:00
/lib/modules/6.1.8-3.0.0.7.oe1.aarch64/build ->
/usr/src/kernels/6.1.8-3.0.0.7.oe1.aarch64
In this case, current configure will put kernel's Module.symvers to
variable KBUILD_EXTRA_SYMBOLS. This should be avoided after kernel
v5.19 which contains commit "b8422711080f modpost: make multiple export
error". This making multiple export symbol as an error from a warning
which can be seen in the config.log:
...
ERROR: modpost: vmlinux: 'init_uts_ns' exported twice. Previous export
was in vmlinux
...

Test-Parameters: trivial
Change-Id: I35295b3acc7fffb93716362f5d8c659eb922afcb
Signed-off-by: Xinliang Liu <xinliang.liu@linaro.org>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50399
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>