qemu tests/unit/test-vmstate crashes in g_tree_foreach
Description of problem:
qemu test suite crashes with the latest Fedora Rawhide.
Downstream issue: https://bugzilla.redhat.com/show_bug.cgi?id=2173639
Steps to reproduce:
1. Compile and test qemu from source as normal.

```
214/658 qemu:unit / test-vmstate                                                  ERROR           0.22s   killed by signal 11 SIGSEGV
317/658 qemu:qtest+qtest-i386 / qtest-i386/rtl8139-test                           ERROR           0.28s   2 subtests passed
588/658 qemu:qtest+qtest-x86_64 / qtest-x86_64/rtl8139-test                       ERROR           0.45s   2 subtests passed
```

The stack trace from the test is:

```
#0  g_tree_foreach (user_data=0x7fffa23ccbc0, func=0x55a834fe3770 <diff_tree>, 
    tree=<optimized out>) at ../glib/gtree.c:1132
#1  g_tree_foreach (tree=<optimized out>, func=0x55a834fe3770 <diff_tree>, 
    user_data=0x7fffa23ccbc0) at ../glib/gtree.c:1117
#2  0x000055a834fe382c in compare_trees (tree1=0x55a836723bf0, 
    tree2=0x55a836723f50, 
    function=function@entry=0x55a834fe3570 <match_interval_mapping_node>)
    at ../tests/unit/test-vmstate.c:1085
#3  0x000055a834fee265 in diff_domain (d2=0x55a836709310, d1=0x55a836708fd0)
    at ../tests/unit/test-vmstate.c:1093
#4  test_gtree_load_domain () at ../tests/unit/test-vmstate.c:1138
#5  0x00007f0eef39d32e in test_case_run (tc=0x55a836724150)
    at ../glib/gtestutils.c:3108
#6  g_test_run_suite_internal (suite=suite@entry=0x55a8367056e0, 
    path=path@entry=0x0) at ../glib/gtestutils.c:3203
#7  0x00007f0eef39cf03 in g_test_run_suite_internal (
    suite=suite@entry=0x55a836705090, path=path@entry=0x0)
    at ../glib/gtestutils.c:3222
#8  0x00007f0eef39cf03 in g_test_run_suite_internal (
    suite=suite@entry=0x55a8366ff670, path=path@entry=0x0)
    at ../glib/gtestutils.c:3222
#9  0x00007f0eef39cf03 in g_test_run_suite_internal (
    suite=suite@entry=0x55a836700140, path=path@entry=0x0)
#10 0x00007f0eef39d8c2 in g_test_run_suite (suite=0x55a836700140)
    at ../glib/gtestutils.c:3302
#11 0x00007f0eef397c40 in g_test_run () at ../glib/gtestutils.c:2409
#12 g_test_run () at ../glib/gtestutils.c:2396
#13 0x000055a834fe2645 in main (argc=<optimized out>, argv=<optimized out>)
    at ../tests/unit/test-vmstate.c:1523
```

This can also be reproduced in gdb using a command similar to:

```
$ MALLOC_PERTURB_=175 G_TEST_SRCDIR=/home/rjones/d/qemu/tests/unit G_TEST_BUILDDIR=/home/rjones/d/qemu/build/tests/unit gdb --args /home/rjones/d/qemu/build/tests/unit/test-vmstate --tap -k
...
(gdb) run
Thread 1 "test-vmstate" received signal SIGSEGV, Segmentation fault.
g_tree_foreach (user_data=0x7fffffffd3e0, func=0x555555568770 <diff_tree>, tree=<optimized out>) at ../glib/gtree.c:1132
1132	      if ((*func) (node->key, node->value, user_data))
(gdb) bt
#0  g_tree_foreach (user_data=0x7fffffffd3e0, func=0x555555568770 <diff_tree>, 
    tree=<optimized out>) at ../glib/gtree.c:1132
#1  g_tree_foreach (tree=<optimized out>, func=0x555555568770 <diff_tree>, 
    user_data=0x7fffffffd3e0) at ../glib/gtree.c:1117
#2  0x000055555556882c in compare_trees (tree1=0x5555555ccdb0, 
    tree2=0x5555555cd110, 
    function=function@entry=0x555555568570 <match_interval_mapping_node>)
    at ../tests/unit/test-vmstate.c:1085
#3  0x0000555555573265 in diff_domain (d2=0x5555555b3310, d1=0x5555555b2fd0)
    at ../tests/unit/test-vmstate.c:1093
#4  test_gtree_load_domain () at ../tests/unit/test-vmstate.c:1138
#5  0x00007ffff7eb132e in test_case_run (tc=0x5555555cd310)
    at ../glib/gtestutils.c:3108
#6  g_test_run_suite_internal (suite=suite@entry=0x5555555af6e0, 
    path=path@entry=0x0) at ../glib/gtestutils.c:3203
#7  0x00007ffff7eb0f03 in g_test_run_suite_internal (
    suite=suite@entry=0x5555555af090, path=path@entry=0x0)
    at ../glib/gtestutils.c:3222
#8  0x00007ffff7eb0f03 in g_test_run_suite_internal (
    suite=suite@entry=0x5555555a9670, path=path@entry=0x0)
    at ../glib/gtestutils.c:3222
#9  0x00007ffff7eb0f03 in g_test_run_suite_internal (
    suite=suite@entry=0x5555555aa140, path=path@entry=0x0)
    at ../glib/gtestutils.c:3222
#10 0x00007ffff7eb18c2 in g_test_run_suite (suite=0x5555555aa140)
    at ../glib/gtestutils.c:3302
#11 0x00007ffff7eabc40 in g_test_run () at ../glib/gtestutils.c:2409
#12 g_test_run () at ../glib/gtestutils.c:2396
#13 0x0000555555567645 in main (argc=<optimized out>, argv=<optimized out>)
    at ../tests/unit/test-vmstate.c:1523
```

Unfortunately so much is "optimized out" that it's hard to tell what's going wrong.