libstdc++: Force _Hash_node_value_base methods inline to fix abi (PR111050)

libstdc++: Force _Hash_node_value_base methods inline to fix abi (PR111050)

https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=1b6f0476837205932613ddb2b3429a55c26c409d
changed _Hash_node_value_base to no longer derive from _Hash_node_base, which means
that its member functions expect _M_storage to be at a different offset. So explosions
result if an out-of-line definition is emitted for any of the member functions (say,
in a non-optimized build) and the resulting object file is then linked with code built
using older version of GCC/libstdc++.

libstdc++-v3/ChangeLog:

	PR libstdc++/111050
	* include/bits/hashtable_policy.h
	(_Hash_node_value_base<>::_M_valptr(), _Hash_node_value_base<>::_M_v())
	Add [[__gnu__::__always_inline__]].

(cherry picked from commit 2c1e3544a94c5d7354fad031e1f9731c3ce3af25)