[gdb/testsuite] Fix some gdb.dwarf2 test-cases for check-read1

I ran the testsuite in an environment simulating a stressed system in
combination with check-read1.  This exposes a few more FAILs.

Fix the gdb.dwarf2 ones by using pipe / grep to filter out unnecessary output.

Tested on x86_64-linux.

gdb/testsuite/gdb.dwarf2/backward-spec-inter-cu.exp

@@ -98,6 +98,7 @@ foreach_with_prefix worker_threads $worker_threads_list {
 
     gdb_load $binfile
 
-    gdb_test "maint print objfiles" "$eol$ws+qualified:$ws+ns::v$eol.*" \
+    gdb_test "pipe maint print objfiles | grep ns::v" \
+	"$ws+qualified:$ws+ns::v" \
 	"v has parent ns"
 }

gdb/testsuite/gdb.dwarf2/forward-spec-inter-cu.exp

@@ -98,6 +98,7 @@ foreach_with_prefix worker_threads $worker_threads_list {
 
     gdb_load $binfile
 
-    gdb_test "maint print objfiles" "$eol$ws+qualified:$ws+ns::v$eol.*" \
+    gdb_test "pipe maint print objfiles | grep ns::v" \
+	"$ws+qualified:$ws+ns::v" \
 	"v has parent ns"
 }

gdb/testsuite/gdb.dwarf2/gdb-index.exp

@@ -95,7 +95,13 @@ proc local_add_gdb_index { program } {
 # building an index from a program already using one.
 
 set test "check if index present"
-gdb_test_multiple "mt print objfiles ${testfile}" $test {
+set filter "gdb_index|debug_names|Psymtabs|Cooked"
+set cmd "pipe mt print objfiles ${testfile} | grep -E \"$filter\""
+set cmd_re [string_to_regexp $cmd]
+gdb_test_multiple $cmd $test {
+    -re ^$cmd_re {
+	exp_continue
+    }
     -re "gdb_index.*${gdb_prompt} $" {
 	set binfile_with_index $binfile
 	set host_binfile_with_index [gdb_remote_download host $binfile]

gdb/testsuite/gdb.dwarf2/pr13961.exp

@@ -36,7 +36,8 @@ gdb_test "break -q main" "Breakpoint.*at.*"
 pass $testfile
 
 # Regression test for PR symtab/30739.
-gdb_test_multiple "maint print objfiles $binfile" "no foo::foo" {
+set cmd "pipe maint print objfiles $binfile | grep foo::foo"
+gdb_test_multiple $cmd "no foo::foo" {
     -re -wrap "\r\n *qualified: *foo::foo\r\n.*" {
 	fail $gdb_test_name
     }

gdb/testsuite/gdb.dwarf2/self-spec.exp

@@ -59,8 +59,8 @@ require {string eq $index ""}
 
 require !readnow
 
-gdb_test "maint print objfiles $testfile" \
-    "\r\n *qualified: *c1\r\n.*" \
+gdb_test "pipe maint print objfiles $testfile | grep c1" \
+    " *qualified: *c1" \
     "class c1 in cooked index"
 
 gdb_test "maint expand-symtabs"