libstdc++: Add always_inline to most allocator functions

libstdc++: Add always_inline to most allocator functions

This reduces the abstraction penalty for allocator support in
unoptimized code. Constructing and using allocators in containers calls
many one-line (or completely empty) inline functions. Those can all be
inlined to reduce code size and function call overhead for -O0.

libstdc++-v3/ChangeLog:

	* include/bits/alloc_traits.h (allocator_traits): Add
	always_inline attribute to all member functions.
	(__do_alloc_on_copy, __alloc_on_copy, __do_alloc_on_move)
	(__alloc_on_move, __do_alloc_on_swap, __alloc_on_swap)
	(_Destroy(FwdIter, FwdIter, allocator<T>&)): : Add
	always_inline attribute.
	* include/bits/allocator.h (allocator): Add always_inline
	attribute to all member functions and equality operators.
	* include/bits/new_allocator.h (__new_allocator): Likewise.
	* include/ext/alloc_traits.h (__gnu_cxx::__alloc_traits):
	Likewise.