AC_TRY_LINK

[Roland McGrath]

Those tests are necessary to ensure that you have everything you need for
libpthread to work right.  If you need to get around them for bootstrapping
purposes, you can hand-prime a config.cache file to preempt the test.  You
only have to do this in the very first glibc build.  After that you should
be able to have enough installed for a vanilla configure and build to work
right.