gdb::handle_eintr, remove need to specify return type

gdb::handle_eintr, remove need to specify return type

This eliminates the need to specify the return type when using
handle_eintr.  We let the compiler deduce it for us.

Also, use lowercase for function parameter names.  Uppercase should
only be used on template parameters.

gdb/ChangeLog:

	* nat/linux-waitpid.c: Include "gdbsupport/eintr.h".
	(my_waitpid): Use gdb::handle_eintr.

gdbserver/ChangeLog:

	* netbsd-low.cc (netbsd_waitpid, netbsd_process_target::kill)
	(netbsd_qxfer_libraries_svr4): Use gdb::handle_eintr without
	explicit type.

gdbsupport/ChangeLog:

	* eintr.h (handle_eintr): Replace Ret template parameter with
	ErrorValType.  Use it as type of the failure value.  Deduce the
	function's return type using decltype.  Use lowercase for function
	parameter names.