[cxx feature check] what satisfies GNU_POSIX_REGEX | POSIX_REGEX?

trying to compile llvm 11 from source with cmake 3.19, former pulling in Google’s benchmarking https://github.com/google/benchmark/blob/master/CMakeLists.txt#L263 which tests for


and the test fails as apparently neither is available on the node.

since the node is based on the Debian package feed I was trying to find a package that satisfies either one but came up empty.

installed libghc-regex-posix-prof package but that did not help

package gnulib should be satisfactory but it seems that the benchmark code is buggy.