[Bug libstdc++/59177] steady_clock::now() and system_clock::now do not use the vdso (and are therefore very slow)

[luto at mit dot edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59177

--- Comment #12 from Andy Lutomirski <luto at mit dot edu> ---
D'oh!  I assumed that "it" was the resulting library (and thus that it would
require linking *against librt*), not that "it" was the configure test.