google benchmark: on some machines, librt is found (despite it being a unix-only library)

[strega-nil-ms]

In #2780, we have added google benchmark to the build. However, on some machines,

https://github.com/google/benchmark/blob/0d98dba29d66e93259db7daa53a9327df767a415/CMakeLists.txt#L131

finds librt. To get around this, we set HAVE_LIB_RT to OFF in our cmake code, but it would be good to figure out exactly why it's found, given that it should definitely not exist (and results in a build failure):

STL/benchmarks/CMakeLists.txt

Lines 37 to 38 in c34f249

	# TRANSITION, GH-2816: on some machines, librt is found, despite it being a unix-only library
	set(HAVE_LIB_RT OFF)

[StephanTLavavej]

nicole mazzuca (@strega-nil-ms) saw this on two of her machines but Charlie Barto (@barcharcraz) didn't - so this seems to be related to something that's installed on the machines, we just don't know what yet.

[StephanTLavavej]

This workaround was removed by #3151 on 2022-10-24.