[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 #3 from Andy Lutomirski <luto at mit dot edu> ---
I can't get gcc trunk to build right now, but I just distcleaned and rebuilt
the 4.8 branch truck on Fedora 19, which has glibc-2.17-19.fc19.x86_64.  It
defines _GLIBCXX_USE_CLOCK_GETTIME_SYSCALL.  This happens because:

configure:19349: checking for clock_gettime, nanosleep and sched_yield
configure:19378: result: no

I think that the underlying problem is that --enable-libstdcxx-time defaults to
"no".  Shouldn't it default to "yes" (and hence run the fancy configure
checks)?  Configuring with ./configure --enable-libstdcxx-time does the right
thing.