gdb/testsuite: Allow DWARF assembler to create multiple line tables

Fixes a bug in the DWARF assembler that prevents multiple line tables
from being created in a test.  We currently don't initialise a couple
of flags, as a result we will only ever generate one end of file list,
and one end of header, in the first line table.  Any additional line
tables will be missing these parts, and will therefore be corrupt.

This fix will be required for a later commit.  There should be no
change in the testsuite after this commit.

gdb/testsuite/ChangeLog:

	* lib/dwarf.exp (Dwarf::lines): Reset _line_saw_program and
	_line_saw_file.

Change-Id: Id7123f217a036f26ee32d608db3064dd43164596

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2020-01-13  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* lib/dwarf.exp (Dwarf::lines): Reset _line_saw_program and
+	_line_saw_file.
+
 2020-01-13  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* lib/tuiterm.exp (Term::_check_box): Check some parts of the top

gdb/testsuite/lib/dwarf.exp

@@ -1309,6 +1309,8 @@ namespace eval Dwarf {
 	set is_64 0
 	set _unit_version 4
 	set _unit_addr_size default
+	set _line_saw_program 0
+	set _line_saw_file 0
 
 	foreach { name value } $options {
 	    switch -exact -- $name {