[libcxx-dev] Test failures for system with no threads

[Hafiz Abid Qadeer via libcxx-dev]

Hi,
I test libcxx for baremetal targets and I recently saw many test
failures. Upon investigation, it seems that recent config changes have
altered when available_features is populated. This is causing wrong set
of libraries to be linked. Here are more details:

Previously features like 'libcpp-has-no-threads' were added in the
available_features in parse_config_site_and_add_features
which was called before configure_link_flags. So when control reached
LinuxLocalTI.add_cxx_link_flags (called from configure_link_flags),
available_features was already populated. The add_cxx_link_flags could
check whether feature like 'libcpp-has-no-threads' is present or not and
link -lpthread accordingly

After recent changes, the 'available_features' is populated in
newconfig.configure which is called after configure_link_flags. As a
result, when add_cxx_link_flags is called, the 'available_features' is
empty and add_cxx_link_flags always calculates enable_threads to be true.

I assume that enable_threads is true on most systems so thats why this
error was not caught. I was testing with LIBCXX_ENABLE_THREADS set to
false so noticed this error.

I am working on a fix unless someone beats me to it. But would
appreciate if somebody who is more familiar with this area can confirm
that my analysis is correct.

Thanks,
-- 
Hafiz Abid Qadeer
Mentor Embedded/CodeSourcery