Fix build of nptl/tst-thread_local1.cc with GCC 12

The test nptl/tst-thread_local1.cc fails to build with GCC mainline
because of changes to what libstdc++ headers implicitly include what
other headers:

tst-thread_local1.cc: In function 'int do_test()':
tst-thread_local1.cc:177:5: error: variable 'std::array<std::pair<const char*, std::function<void(void* (*)(void*))> >, 2> do_thread_X' has initializer but incomplete type
  177 |     do_thread_X
      |     ^~~~~~~~~~~

Fix this by adding an explicit include of <array>.

Tested with build-many-glibcs.py for aarch64-linux-gnu.

(cherry picked from commit 2ee9b24f)