* gthr-win32.h: Wrap all functions in extern "C".
	(__gthread_key_t): Typedef as unsigned long,
	not win32 DWORD.
	(__GTHREAD_ONCE_INIT): Use 0, not win32 FALSE.
	(__gthread_mutex_t): Typedef as void*, not win32 HANDLE.
	(__gthr_win32_once, __gthr_win32_key_create,
	__gthr_win32_key_delete, __gthr_win32_getspecific,
	__gthr_win32_setspecific, __gthr_win32_mutex_init_function,
	__gthr_win32_mutex_lock,__gthr_win32_mutex_trylock,
	__gthr_win32_mutex_unlock): Declare.
	(__gthread_once,__gthread_key_create,
	__gthread_key_delete, __gthread_getspecific,
	__gthread_setspecific, __gthread_mutex_init_function,
	__gthread_mutex_lock,__gthread_mutex_trylock,
	__gthread_mutex_unlock): Call corresponding
	__gthr_win32_* extern implementations if #defined
	__GTHREAD_HIDE_WIN32API.
	* config/i386/t-mingw32 (LIB2FUNCS_EXTRA): Set to
	$(srcdir)/config/i386/gthr-win32.c
	* config/i386/gthr-win32.c: New implementation file.
	(__gthr_win32_once, __gthr_win32_key_create,
	__gthr_win32_key_delete, __gthr_win32_getspecific,
	__gthr_win32_setspecific, __gthr_win32_mutex_init_function,
	__gthr_win32_mutex_lock,__gthr_win32_mutex_trylock,
	__gthr_win32_mutex_unlock): New functions, based on
	static inlines in gthr-win32.h.

From-SVN: r54484