libstdc++: Define some std::string constructors inline

libstdc++: Define some std::string constructors inline

There are a lot of very simple constructors for the old string which are
not defined inline. I don't see any reason for this and it probably
makes them less likely to be optimized away. Move the definitions into
the class body.

libstdc++-v3/ChangeLog:

	* include/bits/basic_string.h (basic_string(const Alloc&))
	(basic_string(const basic_string&)
	(basic_string(const CharT*, size_type, const Alloc&))
	(basic_string(const CharT*, const Alloc&))
	(basic_string(size_type, CharT, const Alloc&))
	(basic_string(initializer_list<CharT>, const Alloc&))
	(basic_string(InputIterator, InputIterator, const Alloc&)):
	Define inline in class body.
	* include/bits/basic_string.tcc (basic_string(const Alloc&))
	(basic_string(const basic_string&)
	(basic_string(const CharT*, size_type, const Alloc&))
	(basic_string(const CharT*, const Alloc&))
	(basic_string(size_type, CharT, const Alloc&))
	(basic_string(initializer_list<CharT>, const Alloc&))
	(basic_string(InputIterator, InputIterator, const Alloc&)):
	Move definitions into class body.