Use clean_restart in gdb.dlang

Change gdb.dlang to use clean_restart more consistently.

gdb/testsuite/gdb.dlang/demangle.exp

@@ -195,10 +195,7 @@ proc test_d_demangling {} {
     test_demangling "_D3std6socket23UnknownAddressReference6__ctorMFPS4core3sys5posix3sys6socket8sockaddrkZC3std6socket23UnknownAddressReference" "std.socket.UnknownAddressReference.this(core.sys.posix.sys.socket.sockaddr*, uint)"
 }
 
-# Start with a fresh gdb.
-
-gdb_exit
-gdb_start
+clean_restart
 
 if [set_lang_d] {
     gdb_test_no_output "set width 0"

gdb/testsuite/gdb.dlang/expression.exp

@@ -127,10 +127,7 @@ proc test_d_expressions {} {
     gdb_test "print \[1, 2\] ~ \[2, 3\]" " = \\\{1, 2, 2, 3\\\}"
 }
 
-# Start with a fresh gdb.
-
-gdb_exit
-gdb_start
+clean_restart
 
 if [set_lang_d] {
     test_d_integer_literals

gdb/testsuite/gdb.dlang/primitive-types.exp

@@ -49,10 +49,7 @@ proc test_builtin_d_types_accepted {} {
     gdb_test "ptype dchar" "type = dchar"
 }
 
-# Start with a fresh gdb.
-
-gdb_exit
-gdb_start
+clean_restart
 
 if [set_lang_d] {
     test_builtin_d_types_accepted

gdb/testsuite/gdb.dlang/properties.exp

@@ -80,10 +80,7 @@ proc test_d_typeof {} {
     gdb_test "ptype typeof(7.0f ^^ 3)" "type = float"
 }
 
-# Start with a fresh gdb.
-
-gdb_exit
-gdb_start
+clean_restart
 
 if [set_lang_d] {
     test_d_sizeof