As detailed in Issue #57642, the test-suite doesn't compile on Solaris.
This patch fixes the compilation issues as explained there.
Tested on amd64-pc-solaris2.11 (8 failures, all fpcmp-target: Comparison failed), sparcv9-sun-solaris2.11 (11 failures, same fpcmp-target errors), and x86_64-pc-linux-gnu (no regressions).
This is a copy of https://github.com/google/benchmark I think. Did you submit those changes for upstream review?