build(macos/other): librt is not needed

[sitano]

Follow up to #20

Since glibc >= 2.17 (2012-12-25), librt is a stub-only library. (https://abi-laboratory.pro/?view=changelog&l=glibc&v=2.17)

• The clock_* suite of functions (declared in <time.h>) is now available directly in the main C library. Previously it was necessary to link with -lrt to use these functions. This change has the effect that a single-threaded program that uses a function such as clock_gettime (and is not linked with -lrt) will no longer implicitly load the pthreads library at runtime and so will not suffer the overheads associated with multi-thread support in other code such as the C++ runtime library.

Current version on Arch Linux is 2.40.

Build results: https://buildbot.mariadb.org/#/grid?branch=refs%2Fpull%2F24%2Fmerge

[sitano]

As it can be seen at least Debian 10, 11, and Ubuntu 20.04 still provide some functions in librt such as timer_create() that is used from check_get_clockid() at libcheck_pic.a(check.o).

[sitano]

The solution could be to include rt lib if timer_create is not found in libc for example, or just exclude it for DARWIN builds.

[sitano]

@grooverdan wdyt?

[sitano]

I think the patch is relatively good. I hope CI builders do build tests :D.
The solution is - lazy link rt lib if it is present in the system for tests that use libcheck.
Can you guys pls restart 2 failed builders due to git tls hs

[gal-s390x-ubuntu-2204](https://buildbot.mariadb.org/#/builders/366)	[failed update (failure)](https://buildbot.mariadb.org/#/builders/366/builds/506)
[gal-s390x-ubuntu-2404](https://buildbot.mariadb.org/#/builders/669)	[failed update (failure)](https://buildbot.mariadb.org/#/builders/669/builds/23)

or maybe give me a permission to press button Rebuild for failed workers? (@grooverdan)

[grooverdan]

Sorry for delay. CMake can do checks. What do you think of this:

CHECK_LIBRARY_EXISTS(rt timer_create "" HAVE_TIMER_CREATE)
IF (HAVE_TIMER_CREATE)
  LIST(APPEND GALERA_UNIT_TEST_LIBS rt)
ENDIF(HAVE_TIMER_CREATE)

[sitano]

@grooverdan I am up for it. What if there will be another function besides timer_create that will be needed from librt and we miss it? If you think it is relatively safe I can replace it easily with your version. What would you say?

[grooverdan]

timer_delete was the only other symbol missing in the link. I assume both where moved at the same time and are now gone. Single symbol test is fine.

I can't easily grant rebuild access so I triggered those.

[sitano]

Ok, changed to CHECK_LIBRARY_EXISTS(rt timer_create "" HAVE_TIMER_CREATE)