2021-04-28  Jonathan Wakely  <jwakely@redhat.com>

	PR libstdc++/100298
	* include/bits/std_thread.h (thread::hardware_concurrency): Add
	missing noexcept to inline definition for non-gthreads targets.

--- libstdc++-v3/include/bits/std_thread.h
+++ libstdc++-v3/include/bits/std_thread.h
@@ -270,7 +270,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #ifndef _GLIBCXX_HAS_GTHREADS
   inline void thread::join() { std::__throw_system_error(EINVAL); }
   inline void thread::detach() { std::__throw_system_error(EINVAL); }
-  inline unsigned int thread::hardware_concurrency() { return 0; }
+  inline unsigned int thread::hardware_concurrency() noexcept { return 0; }
 #endif
 
   inline void