configure: Fixed the problem that librt was explicitly needed in RHEL 6

[yuusuke]

We are building libqb in RHEL 6.
Although there was no problem up to v.1.0.1, since "AC_SEARCH_LIBS ([mq_open], [rt])" was deleted by the following modification, -lrt does not enter LIBS.
Therefore, in RHEL 6, HAVE_MONOTONIC_CLOCK is no longer defined from v 1.0.2.
cb5ee92

Below is the information at v1.0.2 build time.
FYI: Since autogen.sh fails with the combination of v1.0.2 and RHEL6, we backport 9b50aa4.

[root@416fc3aee587 libqb]# git clean -d -x -f; git checkout v1.0.2 -f
HEAD is now at 608de6d... lib: update library version for upcoming 1.0.2 release
[root@416fc3aee587 libqb]# curl -OL https://github.com/ClusterLabs/libqb/commit/9b50aa4e5b84f495207b3f6185a1d6cb68af3f6d.patch && patch -d . -p1 < 9b50aa4e5b84f495207b3f6185a1d6cb68af3f6d.patch
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
103   618    0   618    0     0    773      0 --:--:-- --:--:-- --:--:--   929
patching file m4/ax_compat.m4
[root@416fc3aee587 libqb]# ./autogen.sh && ./configure
(snip)
[root@416fc3aee587 libqb]# less config.log
(snip)
configure:20863: checking for a working clock_getres(CLOCK_MONOTONIC, &ts)
configure:20895: gcc -std=gnu99 -o conftest -g -O2   conftest.c  >&5
/tmp/ccHTz3Ft.o: In function `main':
/usr/local/src/repo/libqb/conftest.c:69: undefined reference to `clock_getres'
collect2: ld returned 1 exit status
configure:20899: $? = 1
(snip)
configure:22464: checking for clock_gettime
configure:22520: gcc -std=gnu99 -o conftest -g -O2   conftest.c  >&5
/tmp/ccHFUrj5.o: In function `main':
/usr/local/src/repo/libqb/conftest.c:113: undefined reference to `clock_gettime'
collect2: ld returned 1 exit status
configure:22527: $? = 1

[kgaillot]

looks good to me

[wferi]

agreed

[knet-ci-bot]

Can one of the admins verify this patch?

[kgaillot]

ok to test

[chrissie-c]

We don't support RHEL6 and I can't even get autogen.sh to work on my RHEL6 VMs because autoconf is out-of-date so I'm not really sure what you're trying to solve here.

However the patch is non-intrusive so I'm not against it.