libstdc++: Use RAII to replace try/catch blocks

libstdc++: Use RAII to replace try/catch blocks

Move _Guard into std::vector declaration and use it to guard all calls to
vector _M_allocate.

Doing so the compiler has more visibility on what is done with the pointers
and do not raise anymore the -Wfree-nonheap-object warning.

libstdc++-v3/ChangeLog:

	* include/bits/vector.tcc (_Guard): Move all the nested duplicated class...
	* include/bits/stl_vector.h (_Guard_alloc): ...here and rename.
	(_M_allocate_and_copy): Use latter.
	(_M_initialize_dispatch): Small code simplification.
	(_M_range_initialize): Likewise and set _M_finish first from the result
	of __uninitialize_fill_n_a that can throw.