Allow "info address" of a template parameter

Allow "info address" of a template parameter

PR symtab/16842 shows that gdb will crash when the user tries to
invoke "info address" of a template parameter.

The bug here is that dwarf2read.c does not set the symtab on the
template parameter symbols.  This is pedantically correct, given that
the template symbols do not appear in a symtab.  However, gdb
primarily uses the symtab backlink to find the symbol's objfile.  So,
this patch simply sets the symtab on these symbols.

Tested by the buildbot.

gdb/ChangeLog
2018-08-02  Tom Tromey  <tom@tromey.com>

	PR symtab/16842.
	* dwarf2read.c (read_func_scope): Set symtab on template parameter
	symbols.
	(process_structure_scope): Likewise.

gdb/testsuite/ChangeLog
2018-08-02  Tom Tromey  <tom@tromey.com>

	PR symtab/16842.
	* gdb.cp/temargs.exp: Test "info address" of a template
	parameter.