[gdb/testsuite] Fix gdb.threads/dlopen-libpthread.exp for upstream glibc

On ubuntu 22.04.1 x86_64, I run into:
...
(gdb) info probes all rtld rtld_map_complete^M
No probes matched.^M
(gdb) XFAIL: gdb.threads/dlopen-libpthread.exp: info probes all rtld rtld_map_complete
UNTESTED: gdb.threads/dlopen-libpthread.exp: no matching probes
...
This has been filed as PR testsuite/17016.

The problem is that the name rtld_map_complete is used, which was only
available in Fedora 17, and upstream the name map_complete was used.

In the email thread discussing a proposed patch (
https://sourceware.org/legacy-ml/gdb-patches/2014-09/msg00712.html ) it was
suggested to make the test-case handle both names.

So, handle both names: map_complete and rtld_map_complete.

This exposes the following FAIL:
...
(gdb) info sharedlibrary^M
From To    Syms Read Shared Object Library^M
$hex $hex  Yes       /lib64/ld-linux-x86-64.so.2^M
$hex $hex  Yes (*)   /lib/x86_64-linux-gnu/libgtk3-nocsd.so.0^M
$hex $hex  Yes       /lib/x86_64-linux-gnu/libc.so.6^M
$hex $hex  Yes       /lib/x86_64-linux-gnu/libdl.so.2^M
$hex $hex  Yes       /lib/x86_64-linux-gnu/libpthread.so.0^M
(*): Shared library is missing debugging information.^M
(gdb) FAIL: gdb.threads/dlopen-libpthread.exp: libpthread.so not found
...
due to using a glibc (v2.35) that has libpthread integrated into libc.

Fix this by changing the FAIL into UNSUPPORTED.

Tested on x86_64-linux.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=17016

gdb/testsuite/gdb.threads/dlopen-libpthread.exp

@@ -40,22 +40,37 @@ if { ![runto_main] } {
     return -1
 }
 
-set test "info probes all rtld rtld_map_complete"
-gdb_test_multiple $test $test {
-    -re "\[ \t\]rtld_map_complete\[ \t\]+0x\[0-9a-f\]+.*\r\n$gdb_prompt $" {
-	pass $test
-    }
-    -re "No probes matched\\.\r\n$gdb_prompt $" {
-	xfail $test
-	untested "no matching probes"
-	return
+set probe_names {}
+# Fedora 17 name.  There's specific code in
+# svr4_find_and_create_probe_breakpoints to deal with this.
+lappend probe_names rtld_map_complete
+# Upstream name.
+lappend probe_names map_complete
+
+set have_probe 0
+foreach probe_name $probe_names {
+    set cmd "info probes all rtld ^$probe_name$"
+    gdb_test_multiple $cmd "" {
+	-re -wrap "\[ \t\]$probe_name\[ \t\]+0x\[0-9a-f\]+.*" {
+	    set have_probe 1
+	}
+	-re -wrap "No probes matched\\." {
+	}
     }
 }
 
+if { !$have_probe } {
+    untested "no matching probes"
+}
+
 set test "libpthread.so not found"
 gdb_test_multiple "info sharedlibrary" $test {
     -re "/libpthread\\.so.*\r\n$gdb_prompt $" {
-	fail $test
+	# With newer glibc, libpthread has been integrated into glibc so we
+	# can expect it to be already loaded at main.  This means we no longer
+	# excercise the scenario we're trying to trigger, but continue
+	# nevertheless.
+	unsupported $test
     }
     -re "/libc\\.so.*\r\n$gdb_prompt $" {
 	pass $test