util: Make qemu_prealloc_mem() optionally consume a ThreadContext

... and implement it under POSIX. When a ThreadContext is provided,
create new threads via the context such that these new threads obtain a
properly configured CPU affinity.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Message-Id: <20221014134720.168738-6-david@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>

include/qemu/osdep.h

@@ -568,6 +568,8 @@ unsigned long qemu_getauxval(unsigned long type);
 
 void qemu_set_tty_echo(int fd, bool echo);
 
+typedef struct ThreadContext ThreadContext;
+
 /**
  * qemu_prealloc_mem:
  * @fd: the fd mapped into the area, -1 for anonymous memory
@@ -582,7 +584,7 @@ void qemu_set_tty_echo(int fd, bool echo);
  * after allocating file blocks for mapped files.
  */
 void qemu_prealloc_mem(int fd, char *area, size_t sz, int max_threads,
-                       Error **errp);
+                       ThreadContext *tc, Error **errp);
 
 /**
  * qemu_get_pid_name: