Fix crash in "finish"

Fix crash in "finish"

PR gdb/28155 notes a crash in "finish" that occurs with a particular
source file compiled by clang.

The bug is the typical gdb problem of a missing call to check_typedef.
clang emits a function whose return type is a typedef to void.
get_return_value asserts that the return type is not void, but the
callers were not using check_typedef first.

gdb/ChangeLog
2019-01-06  Tom Tromey  <tom@tromey.com>

	PR gdb/28155:
	* python/py-finishbreakpoint.c (bpfinishpy_init): Use
	check_typedef.
	* infcmd.c (finish_command_fsm_should_stop): Use check_typedef.
	(print_return_value): Likewise.

gdb/testsuite/ChangeLog
2019-01-06  Tom Tromey  <tom@tromey.com>

	PR gdb/28155:
	* gdb.dwarf2/typedef-void-finish.exp: New file.