Remove symbolp vector

Remove symbolp vector

This removes the symbolp typedef from dwarf2read.c and converts the
associated VEC uses to std::vector.  This fixes a latent possible
memory leak if an exception were thrown, because there were no
cleanups installed for these VECs.

Regression tested on the buildbot.

gdb/ChangeLog
2017-11-08  Tom Tromey  <tom@tromey.com>

	* dwarf2read.c (symbolp): Remove typedef.
	(read_func_scope): Use std::vector.
	(process_structure_scope): Use std::vector.